I've always struggled with Quant, esp Overlapping sets.. in High School, College Stats, and even when I started GMAT prep and he came up with such great techniques to handle questions without getting more confused! Thanks GMAT ninja, you're a true educator & angel!!!
@GMATNinjaTutoring
4 ай бұрын
This absolutely made my day. Thank you so much for the kind words! Have fun studying, and please keep us posted on your progress -- we always like good news. :) - Charles
@Steve_7890
Жыл бұрын
“This video is for you if you like short, middle aged GMAT tutors” genuinely made me laugh. Thanks to Charles and the rest of GMAT Ninja team for the series you brought both for quant and verbal. I really didn’t know where to start my prep from and how to get the right methodologies before discovering your videos!
@GMATNinjaTutoring
Жыл бұрын
Thank you so much, Steven! I'm glad that we could get a chuckle out of somebody. Sometimes, it's hard to laugh when faced with an endless pile of GMAT videos. :) Have fun studying, and keep us posted on your progress!
@bhavanadandu7879
Ай бұрын
Idk about others but I LOVE this middle-aged tutor, I keep hoping Charles pops up when I'm starting any GMAT Ninja video :) It's something about your diction that makes us wanna listen more!
@GMATNinjaTutoring
Ай бұрын
Aw, thank you so much! ❤️
@pierof6837
19 сағат бұрын
Hi All, I ve a question.... About Mixture problems, why are there not videos?
@GMATNinjaTutoring
12 сағат бұрын
When we started writing questions for these videos, we found there just wasn't enough variety in the mixtures questions for them to have their own video. We put questions on mixtures into our statistics video. Check out Q5 in the video linked below for an example of a mixtures question. I hope that helps! Stats video link: kzitem.info/news/bejne/wm6dr5qIo2ObY6wsi=V3DqOv28V7IK6jwm&t=1304
@KARTIKEYBHANDARI-j2n
Ай бұрын
in q9 , how can you introduce x and y to 120 locations when they are just introduced in 90 and 85 respectively
@GMATNinjaTutoring
Ай бұрын
The bars are used twice in this explanation. In the first part, as Charles finds the value of a, the first bar shows the number of locations that introduce item X out of the total of 120. The second bar and third bar do the same for items Y and Z, respectively. In the second part, as Charles finds the value of b, the bars do not represent the number of locations that introduce each item anymore. There are 247 items to introduce (90 locations introduce item X, 85 locations introduce Y, and 72 introduce Z), so Charles says the first bar "uses up" 120 of these items. We could say this was all 90 locations that introduce item X and 30 that introduce item Y. The next bar "uses up" another 120 of these items. We could say that another 55 locations introduce item Y and 65 that introduce item Z. This leaves 7 items that are still to be used up, meaning only 7 locations introduce 3 items. This gives us the value of b, which we can use to find the final answer to this question. I hope that helps!
@LaptopAccount-i3p
Ай бұрын
best teacher ever , hope i get a prof like him wherever i go for MBA
@GMATNinjaTutoring
Ай бұрын
Aw, thank you so much! That absolutely made my day. Have fun studying! - Charles
@vibhorebatwara7221
16 күн бұрын
for q 9 - can the smallest possible number of location who did not introduce all three items be 0?
@GMATNinjaTutoring
14 күн бұрын
No, here's why it can't be zero: We have 120 locations. Ninety of these locations introduce item X. Let's say the 30 locations that don't introduce item X all introduce item y. This means we have 55 locations that must have introduced items X and Y, and 65 locations that have only introduced 1 item. Let's then say that these 65 locations that have only introduced 1 item all introduce item Z. At this point, every location has introduced two items, and we still need another 7 locations to introduce item Z. This means that there must be at least 7 locations that introduce all three items, so the smallest number of locations that introduced all three items must be 7. I hope that helps!
@thesuryapasricha
5 ай бұрын
This is the best video I have ever seen on this topic- OMG! Just like a WOW!!
@GMATNinjaTutoring
5 ай бұрын
This made my day -- thank you so much for the kind words. Have fun studying!
@Anukruti13
3 ай бұрын
great video, I am usually hesitant to go with initiation when it comes to quant because growing up we were taught to follow the formula. I went with intuition for Q8 and 9 got them right! Thank you GMATNinja team!
@GMATNinjaTutoring
3 ай бұрын
I love this. Those are two really tough questions, so I think that's a sign that your intuition might be pretty darned good. Have fun studying, and please keep us posted on your progress!
@nowshinislam1296
4 ай бұрын
In question 6, why can't we just multiply the two probabilities .7*.85 to get the probability of both X and Y occuring? Would this be the solution if the keyword 'least' possible probability wasn't there?
@GMATNinjaTutoring
4 ай бұрын
We can only find the combined probability of two events occurring by multiplying the individual probabilities if we know for certain that the two events are independent. If that was the case, the question would say something to tell you the events were independent. You wouldn't have to infer this; the question would explicitly tell you they were independent. I hope that helps!
@whitemuffins5823
8 ай бұрын
the way you solved the last question was something that opened my eyes. Very very helpful. Thank You!
@GMATNinjaTutoring
8 ай бұрын
Awesome, I'm glad that it was helpful, and thank you so much for the kind words. Have fun studying!
@zahidshuvo007
Жыл бұрын
Excellent class
@minyongkwon5407
5 ай бұрын
In 9th question, how can we spread out? They mentioned that only 90 locations have X. But if we spread out, it means that all 120 locations now have x which is not according to the question.
@manasvitasharma5164
4 ай бұрын
We’re not spreading out. The first counting is the number of places which serve 1 item. The second counting is that of the number of places that serve 2 items. Similarly the third counting is of the number of places that serve 3 items. Since we have to minimise the third counting, we maximise the other 2 and that’s why they are set as 120. Hope that helps!
@ranusingh4636
3 ай бұрын
Please let me know for Q3. I didnt get why you multiplied 15*3 - in no of countings column. I mean what should i infer as 45 ?
@GMATNinjaTutoring
3 ай бұрын
If those 15 people have each visited 3 countries, then 15*3 = 45 countries have been visited. In this question, the final column represents the total number of countries that have been visited. If general if you're using this process, the final column represents the product of the values in the first and second columns. I hope that helps!
@ranusingh4636
3 ай бұрын
@@GMATNinjaTutoring Exactly the word "45 countries" is making me more confused. What I'm thinking is first of all only 3 countries are there how come 45 countries have been visited then? Next ,I think that those 3 countries have been visited 45 times. Please correct my thinking!
@GMATNinjaTutoring
3 ай бұрын
It might help to think of the 45 as representing the number of visits that have occurred. If 15 people have each visited 3 countries, then 45 visits have taken place. Does that make things more clear?
@PrathamS25
7 ай бұрын
Q9. is there an alternate method for calculating minimum. I am unable to process this one properly. Can this question be done using 3-way venn diagram in some way?
@akankshagoel7984
8 ай бұрын
For the last question, is there a possibility that some locations didn't introduce any item(x,y or z)? Cuz only then 72 introduced all will fit into the venn diagram of total 120 locations.
@GMATNinjaTutoring
8 ай бұрын
It is possible for some locations to introduce none of the three items. Consider the scenario in which 72 locations introduced all three items, another 13 introduced item X and Y only, and a further 5 introduced item X only. In this scenario, there are 30 locations that didn't introduce any of the three items. I hoe that helps!
@iluvbrowniesandfudge
7 ай бұрын
I'm still not clear about the solution to the last problem. By bucketing the dishes all together, I think there is some loss of information that changes the answer. If we keep the X, Y and Z information, we can construct a scenario where there are no restaurants with all 3. First, assign X: 90 have it (X) and 30 do not (NX). Then, assign Y strategically to the ones that do not have X, to minimize the chance of having all 3. We want to allocate Y to the 30 NX yielding 30 (NX,Y), 55(X,Y), 45 (X,NY) where NY is no Y. Once again we can allocate Z to the shops that do not have both X and Y. We have 75 slots where there is only X or only Y (30 (NX, Y) + 45 (X, NY)) , and we have 72 Z, so we can "consume" all Z in these slots such that no restaurant has X, Y, and Z.
@GMATNinjaTutoring
7 ай бұрын
Unfortunately, there's a small mistake in your arithmetic. If we assign X to 90 restaurants, then 30 do not have X (NX). We can then assign Y in a way that minimizes the chance of a restaurant having all three. This will give 30 (NX, Y), 55 (X, Y), and *35* (X, NY). This is the point where you make the mistake in your arithmetic as 30 + 55 + 45 = 130, which is too many restaurants. Assigning Z in a way that minimizes the number of restaurants that have all three items, we have 30 (NX, Y, Z) 35 (X, NY, Z) 48 (X, Y, NZ), and 7 (X, Y, Z). So the smallest number of restaurants that have all three items is 7. I hope that helps!
@iluvbrowniesandfudge
7 ай бұрын
thanks so much for the prompt response! sorry for the confusion with my arithmetic error. I'll try watching again to try to understand your much more elegant solution intuitively @@GMATNinjaTutoring
@eldaralizade1707
9 күн бұрын
@@GMATNinjaTutoring Thank you so much for the clarification. I struggled for literally 10 minutes to wrap my head around this question, yet this comment saved me. Thank you for your wonderful videos and contributions to the GMAT community!
@kanikamalhotra818
8 ай бұрын
Bigggggggg thanks for this video! I learnt many new things 🤩
@GMATNinjaTutoring
8 ай бұрын
Thank you, Kanika! Have fun studying.
@KanupriyaSharma-en4ep
2 ай бұрын
Q9 : I am following below approach please correct my mistake No of countings = 247 locations that introduce 1 item = x locations that introduce 2 items = y locations that introduce 3 items = z x+2y+3z = 247 - (1) x+y+z = 120 - (2) using (1) and (2) (x+y+z) + y +2z = 247 120+y+2z = 247 y+2z = 127 maximizing z => y =1 2z = 126 z=63 this should be the max value ? What is wrong in this approach if we negate x+y+z = 120 then how are we concluding that this is a double counting problem
@GMATNinjaTutoring
2 ай бұрын
The mistake occurs when you think that every one of the 120 locations must introduce one of the new items. Take a look at the bar diagram that Charles finishes drawing on the board at 55:15 -- in this scenario, 30 of the 120 locations introduce none of the three items, and this number will change depending on how you arrange which locations introduce items X, Y, and Z. This means you'll need another variable, let's say w, for the locations that introduce 0 items. However, I think the algebra is going to get very messy. I think you'll end up with something like y + 2z - w = 127 if you try to go down the same path, and maximizing z from that equation is going to get really difficult. I'm sorry your method didn't work out as it would have made a brilliant, neat solution. I hope that helps!
@KanupriyaSharma-en4ep
2 ай бұрын
@@GMATNinjaTutoring but if we make case for 0 location as well how do we know this is a double counting problem then
@GMATNinjaTutoring
2 ай бұрын
I'm sorry, I'm not sure what you mean in your question -- what do you mean by a double counting problem? Could you please rephrase the question, and I'll do what I can to help? Thank you!
@ishun2621
5 ай бұрын
You are a blessing in disguise for me !
@GMATNinjaTutoring
5 ай бұрын
Thank you so much, and have fun studying!
@shirleyeriko6012
6 ай бұрын
Q9. Can anyone tell me what is the meaning of "120" and why we can minus 120 twice from 247.
@shirleyeriko6012
6 ай бұрын
My answer was like min of overcount of (3) = total counting - max overcount of (2) = 247- max overcount of (xy or xz or yz) = 247 - (85+72+72)=18. 18/3=6=b. So wrong.
@lynaelayoubi3853
2 жыл бұрын
thanks a lot!!!!! so helpful
@KARTIKEYBHANDARI-j2n
Ай бұрын
hey in q4 statement 1 , just talks about the people who eat joll of rice , but you can not figure out the people who just eat suya . the remaining 60 people can be eating suya and suya and joll of rice , please clarify
@GMATNinjaTutoring
Ай бұрын
As Charles shows in the video from about 21:30, we can use the information in statement (1) to find the number of people who eat suya but not jollof rice. This means statement (1) is sufficient to answer this question. Check out that part of the video, and please let me know if you have any questions. I hope that helps!
@KARTIKEYBHANDARI-j2n
Ай бұрын
@@GMATNinjaTutoring Thank you for the quick response! appreciate it
@rejoicingGrace
2 жыл бұрын
Another great tutoring video with good questions! Warning: be careful with the fourth question, fifth, seventh, eighth and ninth! (Almost all in the second half ha)
@deansakata8619
2 жыл бұрын
these Qs are brutalll😅 but fun!
@yatibansal6654
Жыл бұрын
In question 8, in 2nd approach with table why are we counting against 2nd ranking as 2x, it is not like these people ranked it twice. I understand why we did that in question 3 because if we place these people in real scenario they would account for 2 or 3 different countries but why are we using the same approach here?
@agnelpaul3645
7 ай бұрын
Did you get the answer?
@agnelpaul3645
7 ай бұрын
There is double counting happening since total no. Of people not placing beach @1st rank is 54. Now when you look at the number of people placing either ski or city ahead, it comes to 66 people. This means there are some people who place ski AND city ahead of the beach. This means that 12 people ( 66 - 55) have to be common among the group of people placing ski and the group of people placing city before beach. Hope this helps
@alexdodenhoff8647
Жыл бұрын
For question 8, could you have set up the same matrix as before, where the y axis has columns for the number of people who ranked city trips higher than beach trips, and those who did not. And the x axis has rows for the number of people who ranked ski trips higher than beach trips and those who did not. You put the number who ranked beaches first in the cell that represents the number who ranked neither ski trips nor city trips higher than beach trips and the rest falls into place.
@subramaniaraja3327
7 ай бұрын
Very different perspective and amazingly out of box. Thanks for sharing.
@shirleyeriko6012
6 ай бұрын
Genius
@user-tp4fv5qn7n
7 ай бұрын
In Q7, you could have, other than those who don't say if they approve A, those who don't approve A. So 275+K, where K is composed by those who don't approve A. Where am I wrong?
@GMATNinjaTutoring
7 ай бұрын
If someone did not say they approve of A, then they either disapprove of A or are neutral about it. Those who do not approve of A are already encapsulated in the 275 people we were given in the question, so there's no need for the +K. I hope that helps!
@user-tp4fv5qn7n
7 ай бұрын
ah okay, thank you very much! I thought that if you don't say it means that you're neutral. @@GMATNinjaTutoring
@viren3948
2 жыл бұрын
I got the Q6 on my actual GMAT as questions no 3. I couldn't figure out that it could be solved simply through a 2X2 matrix.
@anshlaroia9443
2 жыл бұрын
Hey! How did your GMAT Go?
@TheAmigoBoyz
5 ай бұрын
For Q6 i thought in terms of Venn diagrams. If we have two probabilities we do not know if they are laying exactly on top of eachother or if they are apart. However, the question essentially asks us for what is the lowest probability of both of them happening, which we could rephrase to "how far can we pull these two Venn sets apart, minimizing the overlap". Since we know that probabilities always have to add to 1, we can add the two probabilities, and identify the overlap that we must at minimum have. 0.7+0.85=1.55, meaning that 0.55 is the minimum overlap. Not sure if it makes sense? It allowed me to solove the problem at least -Actually the more that i think about it, the stem does not say if these events are independent or not, so in theory they could be disjoint events. There could be a possibility of zero that they both occur, so i think the question is flawed
@GMATNinjaTutoring
5 ай бұрын
Your Venn diagram method is a great alternative way of thinking about this question, thank you for sharing it! The two events cannot be disjoint given the answer you found for the minimum overlap. If we assume they were disjoint and the individual probabilities remained as they're written in the question then the total probability in the sample space would be at least 1.55. This is the minimum possible total probability in this scenario because we still have to add on the probability of neither event occurring. Since we can't have a total probability greater than 1, these two events cannot be disjoint. The maximum probability of both events occurring is 0.7, so the range of possible probabilities for both events occurring is 0.55 - 0.7. Since the product of the two probabilities (0.595) is within that range, the two events could be independent. However, we don't need to know whether they are independent or not to answer this question. I hope that helps!
@sannabansal5548
2 жыл бұрын
I dont think the answer of the third question makes sense. I solved using equations and it is coming very different. Please clarify
@GMATNinjaTutoring
2 жыл бұрын
There are always multiple ways to approach any individual GMAT question, so it's certainly possible to use a different sort of algebra to arrive at the correct answer. The answer presented in the video is definitely correct, and we happened to get there using a method that works well for us and for many of our students. If that particular way of thinking doesn't resonate with you, no worries -- there are other ways to answer the question that are perfectly effective, if potentially a bit less efficient. If you arrived at a different answer using algebra, it's probably because there was a mistake somewhere in your equations or calculations. I can't guess what, exactly, your mistake was, though. I hope that helps a bit!
@alexdodenhoff8647
Жыл бұрын
For question 6, could you also use the following method, p(X or Y) = p(X) + p(Y) - p(Both) and because p(X) + p(Y) is 0.55 greater than 1, we say the minimum for both is 0.55
@ashishsinha9035
Жыл бұрын
Muy bien Mr. Charles.
@a_k_s_h_a_r_a_
6 ай бұрын
@Charles Thank you for the video, love your teaching. Q9- you say that (the max) a is 72 which is the minimum of {90,85,72}. Why is this the case? I understood why b is 7 but not why a is 72...
@GMATNinjaTutoring
6 ай бұрын
From the question, we know that 72 of the restaurants introduce item Z. This is the upper limit for the number of restaurants that introduce all three items as a restaurant can't introduce all three items without introducing item Z. This upper limit can be reached if all 72 of the restaurants that introduce item Z also introduce items X and Y. I hope that helps!
@banafshehz6390
11 ай бұрын
Hi thank you for all the videos, I really don't understand how we found out that b=7 in the last question what are those 120 in the first and second place? 120 could only introduce x/y ?! please clarify that for me. BTW I solved it correctly but this way: we know a=72 so b could be anything >0 and as b must be smallest possibility, the greatest answer choice is the answer 😁
@CarmenHorse
Жыл бұрын
On Q8, how does the 10% from 55 (the total of people who ranked other stuff ahead of the beach) minus 45 (total people who did not rank the beach as #1) represent people who ranked beach last? Doesn’t that 10% just count as the double counted group? How did that end up being the group that ranked beach last?
@kanikamalhotra818
8 ай бұрын
Yeah same question @GMATNinjaTutoring
@agnelpaul3645
7 ай бұрын
Q7. Isnt approve of neither A or B implies not approve of A or B. Like for eg if i say to a waiter i approve of neither salad nor desert, the waiter would definity NOT bring salad or desert, he wont bring the salad and desert to see if im neutral or not regarding it. Like am I missing something. Please help.
@GMATNinjaTutoring
7 ай бұрын
If I do not approve of A, it doesn't necessarily mean that I disapprove of it. It might mean that I'm neutral about A. Similarly, if I do not approve of B, I might disapprove of B but I might just be neutral about it. So if I approve of neither A nor B, then I might disapprove of both of them, I could be neutral about both of them, or I could be neutral about one and disapprove of the other. The important thing is that I do not approve of A and I do not approve of B. Following that thought proess means we can fill in the "dis/neutral A" and "dis/neutral B" box with the 325 we're given in statement (2) and from there, we can fill in the rest of the table. This means statement (2) is sufficient to answer this question. I hope that helps!
@agnelpaul3645
7 ай бұрын
@@GMATNinjaTutoring Thank you!
@cheese3729
6 ай бұрын
Great video, thank you so much! For this last question, with the logic presented, there's a suggestion that 113 (120-7) restaurants have two menu items presented. Is this possible, however, given the values of X, Y, and Z? Assuming 7 restaurants have all 3, that leaves 83 introducing X, 78 introducing Y, and 65 introducing Z. These values suggest a maximum of 83 restraunts having 2 of the items presented (for example, 78 have X&Y, and then 5 have X&Z). I must be missing something in understanding the logic behind the maximum calculation, but I just can't crack it. Any guidance would be amazing. Thanks so much!
@RahulKumarSinha2000
6 ай бұрын
First of all, forget ur way of solving this question so that ur way of doing doesn't mix up with my way in order to understand the way I did this 😂 & please give proper gaps at the places where I have inserted *comma* to understand this solution in the way I perceived it. 90,85 & 72 introduced but in total there are 120 franchises(locations) which implies only one item, can be introduced, at 120 locations maximum. Similarly, maximum 120 franchises can introduce exactly 2 items and then we are left with 7 items which can be introduced at 7 franchises. We did so because we wanted to minimize exactly 3 items' locations. In order to do that we'll have to maximize the remaining (exactly 1 & exactly 2). So, we did in this way. Hope this helps and if u r having still having any doubt, plz reply back.
@johndoe12324
2 ай бұрын
Yeah, I agree with your input as well. The approach doesn't make sense if you look at it this way. Could GMAT Ninja offer some clarification?
@user-qq5ue8vx1w
10 ай бұрын
Hey! in Question 6 - if we ask what is the maximum possible value (instead of least possible value), would the answer be 0.7?
@GMATNinjaTutoring
10 ай бұрын
Yes, it would!
@tanyagupta2579
10 ай бұрын
In question 3, the question related to how many people visited each country…… how did you take the random variable 45? Why 45 ? Why not any other digit?
@GMATNinjaTutoring
10 ай бұрын
The 45 in the solution wasn't chosen randomly. If 15 people each visit three countries, then 15*3 = 45 countries will be visited. In a similar fashion, Charles put an X in the table for the number of people that visited two countries each. If X people each visit two countries, then X*2 = 2X countries will be visited. And if (84 - X) people each visit one country, then (84 - X) * 1 = 84 - X countries will be visited. The numbers in this final column should sum to 123, as we know that's the number of "countings" or total number of countries that have been visited. I hope that helps!
@tanyagupta2579
10 ай бұрын
@@GMATNinjaTutoringthankyou. 😳
@abdur5908
Жыл бұрын
n the third question , I took the names of the countries in different columns and hit a dead end. How do you know which categories to take in the double matrix columns ?
@GMATNinjaTutoring
Жыл бұрын
Yup, you'll definitely hit a dead-end if you try to force Q3 into the type of double matrix that we used on Q1 and Q2. The double matrix only works if you have a pair of things that are both complementary -- meaning that 100% fit in exactly one of two categories. For example, in Q1, 100% of the population either eats varenyky or they eat no varenyky -- and logically, there are no exceptions. You fit one category or the other, but not both. So those are our two columns. Similarly, everybody either drinks Nemeroff, or they don't. So those are our rows. If you try to apply that same framework to Q3, it simply doesn't work. First of all, there are three countries, not two -- so there's no way to fit the data into the same little matrix. More importantly, those three countries are NOT complementary. We can't say that 100% of the population visits either Latvia OR Lithuania OR Estonia. It's possible to visit none, or exactly one, or all three. So the country names simply don't work as your columns -- and they won't work in a 2x2 matrix. That's why we use a completely different approach to Q3, as shown in the video. Bottom line: for the double matrix to work, your two columns need to consist of two complementary characteristics that account for 100% of the population, with no overlap. (The same is true of the rows.) If the data doesn't fit that criteria, the double matrix is unlikely to help much. I hope that helps a bit!
@rejoicingGrace
2 жыл бұрын
Charles, I reviewed the final question for several times but still failed to find the value of b. I also tried to use Venn diagram but it was not really helpful. Could you elaborate what the three bars represent? And, what do the two bars represent when you give each of them a value of 120? You said "think of that as the first item in all 120 locations" and "they are getting their second item," but I do not get it. Does the "first item" refer to the product X specifically or just mean "any first product"? Would appreciate your more explanations, thanks!
@GMATNinjaTutoring
2 жыл бұрын
Thank you for the question, Grace! Charles here. I'll be brutally honest: that final explanation isn't the clearest thing I've ever put into a video, unfortunately. To be fair, that last question really doesn't fit terribly well into any of the standard methods that we might apply to overlapping sets questions (either of the chart-type things presented in this video, or Venn diagrams). But still, I should have been clearer about why I was using those bars. Here's how I would think about it: imagine that I have a grand total of 247 menu items. Now, I'm going to start "filling" the menus of 120 locations with those items. First, I'll give each location 1 new item. So I "filled" 120 menus with 1 item each -- and that's what the first bar represents. Then, I'll give each location a 2nd new item. So then I'm "filling" 120 menus with a 2nd item -- and that's what the next bar represents. At that point, I only have 7 new items left to distribute to the restaurants' menus. So only 7 locations need to have all 3 of the new items. And that's what the third and final bar represents. Let us know if that helps? Sorry again for the lack of clarity in the video! And don't worry about this one too much -- it's a rare and challenging variant that you're very, very unlikely to see on your actual exam.
@rejoicingGrace
2 жыл бұрын
@@GMATNinjaTutoring Charles, thanks for your explanations! I actually drew many Venn diagrams for this question but it is a pity that I cannot paste them here--you might find them amusing. I like using Venn diagrams because they are visual. My idea was that if the number of the locations that sell X or Y or Z is 120, 120 should be the result of 247 (X+Y+Z) minus the number of the locations that sell exactly two items, and minus twice the number of the locations that sell all three items. Since I wanted the latter to be as small as possible (I used the variable B to represent the number of locations that sell three items), the former needed to be as large as possible--and I thought that it should be 90-B. So I got one formula: 120=247-(90-B)-2B, and then I got B=37, which is quite different from your answer 7. I think I wrongly set 90-B, since your answer suggests that the number should be 120-B. Your approach is very straightforward, but could I check the following points? 1. When you say you give each of the 120 locations one new item, since no item is introduced by all 120 locations at the same time, could I understand that the first 120 menus should contain at least two items? (For example, the first 90 menus are X item, and the other 30 menus are Y item) 2. After you give each location the second batch of menu, since after this distribution, no location has three menus, the value of b is still 0. And I can imagine that the second batch of 120 menus as 55 menus of Y item and 65 menus of Z item. 3. Now, all locations have gotten two menus individually, but there are only 240 menus in total. The final seven menus (menus of Z item) have to be given to seven locations. So, seven stores would luckily get three types of menus and the value of b is 7. 4. I realize under this approach, if we order the stores from 1st to 120th and give menus in this order, not only the value of b is fixed at 7, the whole distribution situation would remain the same, regardless of which type of menus to be given first. If we give these stores menus of X items first, then menus of Y items and Z items, eventually 7 stores would sell all three items, 48 stores would sell exactly X items and Y items, 35 stores would sell X items and Z items, and 30 stores would sell Y items and Z items. But this distribution situation would not change even if we distribute the menus of Z items first, menus of X items and Y items later. I was very surprised to find out this. Thank you so much for providing this question and the explanations! I do think this question is rare, and so is the way of solution. Right now I cannot imagine how to apply this method to a typical overlapping-set problem. But it is fascinating and eye-opening! Thank you so much!
@GMATNinjaTutoring
2 жыл бұрын
@@rejoicingGrace Haha, I'm glad that you're actually enjoying this, despite its lack of actual value on the GMAT! And yes, the logic you've laid out in #1-4 is correct. You don't really have to worry about the distinction between items X, Y, and Z here, interestingly.
@rejoicingGrace
2 жыл бұрын
@@GMATNinjaTutoring Ha it might be a bit painful but I am really impressed by these creative questions! Look forward to this Friday's session!
@punitmishra6560
2 жыл бұрын
@@GMATNinjaTutoring Thank you for your explanation here. I too didn't understand the video solution but this text solution is lucid.
@anoukuragoda9922
Жыл бұрын
Hi Charles. Hope all is well. I have a question. Why is statement 1 sufficient for the Jollof and Suya rice question? 140 eat Jollof but that includes people who eat Suya too. Aren't we supposed to find the number of people that eat Suya but not Jollof? I got an answer of 4... Choice C. Let me know what you think.
@GMATNinjaTutoring
Жыл бұрын
The key on Q4 is the language in the question itself: all of the 200 residents eat jollof or suya or both. The important part: the phrasing suggests that everybody eats at least one of the foods -- so NONE of them eat neither. That's why I put a big zero in the center square of the chart. Try that, and see if it changes your answer? :) I hope that helps!
@KARTIKEYBHANDARI-j2n
Ай бұрын
@@GMATNinjaTutoring can you please solve it with venn diagram , because I face the same issue and its C for me too . because if you solve it from this perspective , the answer would be different
@corrayatom
8 ай бұрын
Great video Charles ❤ In 42:58 there are two statements both alone are sufficient. But, what if statement was 320, in that case we would get 500-320 = 180 i.e., not 175. What I'm trying to say is that, we are getting an answer from both of the statements but, they are not the same. So, what would be the ans then? A/B/C/D/E 🤔
@GMATNinjaTutoring
8 ай бұрын
Thank you for the kind words! Thankfully, the situation you describe wouldn't happen. In a GMAT data sufficiency question, statement (1) and statement (2) might provide different information, but the scenario will remain consistent throughout the question. In this question, the box for 'approve of policy A' and 'neutral or disapprove of policy B' will be 175 throughout the entire question. You might not be able to find that value from the information provided, but you won't be given any information that changes the value. There is no chance the GMAT would make the value 175 with the information in statement (1) and 180 with the information in statement (2). I hope that helps!
@sachindrabb
9 ай бұрын
Another fantastic video explanation by GMAT Ninja Team. Is there any other method to solve Q6. Please explain in brief
@GMATNinjaTutoring
9 ай бұрын
As in most GMAT Quant questions, there are probably multiple solution paths you could take to solve this problem. The method shown in the video is the way we recommend you solve this problem, but we'd be delighted to hear of others if you have your own way of getting to the right answer. I can think of one way of reasoning through this problem using probability formulas and the understanding that the probability of event X or Y occurring must be less than or equal to one, but that method doesn't provide the certainty that the method in the video provides so I'm not going to list it here. I'm also not going to work through that solution path as it involves probability formulas and this is the overlapping sets video. Let us know if you have an alternative method to solve this question, as we always love hearing of different ways to answer these questions!
@prashantchandra5551
10 ай бұрын
Hi, Unable to adapt the below question using the square matrix method. Can you help: In a class of 50 students, 20 play Hockey, 15 play Cricket and 11 play Football. 7 play both Hockey and Cricket, 4 play Cricket and Football and 5 play Hockey and football. If 18 students do not play any of these given sports, how many students play exactly two of these sports?
@BSA77
Жыл бұрын
for Q6. can I say use this equation: p(X or Y) = p(X) + p(Y) - p(X and Y) which equals to p(X or Y) = 1.55 - p(X and Y). then conclude that p(X and Y) must be at least 0.55 so that 1.55 -0.55 = 1 because p(X or Y) cant be above 1. Can I also take it one step further for the sake of understating and say if p(X and Y) is between (0.55 - 1) (1 being the max for any probability anyways) then p(X or Y) is between 0.55 and 1 ??
@GMATNinjaTutoring
Жыл бұрын
Interesting solution path! I think it works fine in this situation, and if it works better for you than the solution in the video, that's great. I would argue that using the formula is far less intuitive for most test-takers, and the logic shown in the video is probably easier and more versatile. But this totally works, and when you're actually taking the exam, that's all you need!
@BSA77
Жыл бұрын
@@GMATNinjaTutoring yes of course. the method in the video is more intuitive. I was just trying to connect the dots of my earlier learnings. cheers :)
@rahulbajaj8537
Жыл бұрын
Hi @charles, can you please help solving the 3 way sets approach for the below question? For some reason I am not able to get the correct answer? I think I've missed some fundamental When Professor Wang looked at the rosters for this term's classes, she saw that the roster for her economics class (E) had 26 names, the roster for her marketing class (M) had 28, and the roster for her statistics class (S) had 18. When she compared the rosters, she saw that E and M had 9 names in common, E and S had 7, and M and S had 10. She also saw that 4 names were on all 3 rosters. If the rosters for Professor Wang's 3 classes are combined with no student's name listed more than once, how many names will be on the combined roster?
@GMATNinjaTutoring
11 ай бұрын
This is the sort of question that's hard to explain in the limited formatting of a KZitem comment, but I'll do my best. In those 3-way overlapping sets questions, the core idea is that there's some number of actual people, but if we add up the number of "countings" (in your example, the total number of roster spots -- so 26 + 28 + 18 = 72), we'll get a larger number. On these questions, our job is always to disentangle the number of "overcountings". With that general idea in mind, the chart will still work, even though we have different pieces of missing information. You can use the same columns as we do in, say, Q3. The first column is the number of "countings" (classes taken) per person; here, we have people who are in 1, 2, or 3 different classes. The second column is the number of people with that number of classes. And the third column is the "countings" -- so the product of the first two columns. Now, we know that the total "countings" = 72, so that's the sum of the numbers in the third column. We also know that 4 names are on all 3 rosters. And here's the tricky part: how many people are on exactly 2 rosters? Well, 4 people are on all 3 rosters, so 5 are in E & M (but not S), 3 are on E & S (but not M), and 6 are on M & S (but not E). So we have 13 people on exactly 2 rosters. We're almost done now! Let x = the number of people on exactly 1 class roster. Then, all you have to do is multiply across, and you'll be able to solve column 3 for x. And the total number of people will be x + 13 + 4. I hope that helps a bit!
@U_lingo
9 ай бұрын
in Q9 it seems to me that there's something wrong, the max can't be 72 cuz: imagining we had 72 of all three (X, Y & Z), there number of NOT 3 locations of Y would be 85-72=7 , and if we add the surplus to the 90, we'd have 97 restaurants and the total wouldn't reach 120, am I right? (BTW I calculated the max of overlaps of all 3 to be 55)
@GMATNinjaTutoring
9 ай бұрын
If 85 is the number of locations that introduce item Y, and 72 is the maximum number of locations that introduce all three items, then 85-72 tells us the number of locations that introduced item Y but didn't introduce all three items. I'm not sure how that's helpful or what it really tells us. In the text of this question, there is no indication that every location introduces at least one item. It's possible there are several locations that do not introduce an item at all. So, we could have 72 locations that introduce all three items, 13 that introduce items X and Y only, 5 that introduce item X only, and 30 that introduce none of the three items. This adds up to 120 and gives us the maximum number of locations that introduce all three items. I hope that helps!
@ARM26878
Жыл бұрын
Hi Charles: can u please make a video on 3 way basic/advance using your method? Thanks
@GMATNinjaTutoring
Жыл бұрын
We certainly could, but I worry that it might be pretty redundant with this video. Three-way overlapping sets questions aren't terribly common on the GMAT to begin with, and when you do see them, they'll usually look like Q3 in this video. It's vaguely possible -- but pretty unlikely -- that you'll see a more exotic three-way overlapping sets question that looks a bit like #7 (which is arguably a two-way question in disguise) or #8. So if we did another video exclusively on the three-way questions, it would basically be repeating things that look a whole lot like #3, #7, and #8. I'm not sure that it would be very valuable for students, but if enough test-takers think it would be useful, we could give it a shot. :) Have fun studying, Ankush!
@basharabuein409
9 ай бұрын
Hi Charles, thanks again for being an amazing teacher. Love this series! In Q8, after watching the video, the solution makes a lot of sense. However, I am 1000% sure that, on my own, I wouldn't have been able to deduce the table for #of countings/person where "countings" represents the "number of things ahead of beach holiday". How do I come up with these definitions in 3-way questions? Thanks!
@GMATNinjaTutoring
9 ай бұрын
You're welcome! We're so pleased you're enjoying the series. Unfortunately, you're asking the $64,000 question here and the disappointing answer is that it depends entirely on the question. The headings in the table are designed to be as general as possible, so while you might have to change "people to something else in a different question, "countings" can be applied to any question. This means you should be able to build a table that looks similar, if not identical, in structure to the one demonstrated here. However, the thinking behind linking "countings" to "the number of things ahead of beach holidays" is the challenge in this question. Hopefully having seen how Charles does it here, you'll be in a better position to do it next time you see a question like this. I'm sorry that's not a brilliant answer but if it's any consolation, the chances of you seeing a question like this are very slim. I hope that helps a little bit, but please let us know if you have any follow-up questions!
@someshshahi
Жыл бұрын
Hey Charles, how do use the 3 way method if the at least one is not given and neither a,b,c is an option?
@GMATNinjaTutoring
Жыл бұрын
If you take one of the 3-way questions in the video and change it so that people can do NONE of the activities, the question wouldn't be solvable at all. In theory, you could still organize the information using the method in the video, but you'll end up with too many unknowns -- if you're really curious, try it out, and watch what happens. Basically, you'll end up with three variables, and you'll have a mess on your hands. In other words: you won't see a problem quite like that on the GMAT, where you could have people doing 0, 1, 2, or 3 of the activities. So don't lose too much sleep over it. I hope that helps!
@someshshahi
Жыл бұрын
@@GMATNinjaTutoring Thank you for the quick response. I've come across questions in which they provide the neither in the option and then they ask for 2's only. So it's not an additional variable but an additional number so should be solvable right? Also, the way I'm thinking about it is for 'neither option' wouldn't the left most column be 0 in the above method which would lead to (incorrectly so) as the '# of counting as = 0 multiplied by # of people in neither = 0 In addition to this, could the method in the video be used if we are not given the number of people who have chosen 2 options only (exclusive of people who have chosen 3) i.e we are given people who have done two tasks (which includes people who could have also done 3 of the tasks)? Again, thanks for taking the time out for these replies. Regards
@GMATNinjaTutoring
Жыл бұрын
@@someshshahiSure, it's totally possible to have "neither" as a possibility. For example, you could have 0, 1, and 2 in the left-hand column of the chart instead of 1, 2, and 3. That would be solvable using the exact same method as in the video. But it won't work to have FOUR rows in the chart. For example, if we removed the phrase "every traveler has visited at least one" from Q3, the question would no longer be solvable. If you're bored and want to give it a try, go for it. :) Beyond that, I don't think there's any value in inventing tons of hypothetical versions of this question type. The GMAT can certainly be creative in coming up with new variations on questions, but these "three-way" overlapping sets questions are rare to begin with -- fewer than a dozen have ever been released publicly, out several thousand official quant questions. So it's somewhat unlikely that you'll see one of these on your exam at all -- and it's incredibly unlikely that you'll see a variation that goes beyond what we've described in the video. It's theoretically possible, but I wouldn't lose any sleep over it. I hope that helps a bit!
@breakingbad3614
Жыл бұрын
Hi Charles. thanks for informational video. I have a query for Q.9. In case when greatest number of locations that introduced all 3 items is considered; if we take a =72 then i am not able to find values of exactly 1 and exactly 2 location's numbers. Following is the way how i solved, ex 1= number of stores with exactly 1 locations and similarly for ex2 and ex3 ex1 + ex2 + ex3 = 120 and ex1 + 2ex2 + 3ex3 = 247. Now if ex3 = 72 then both equations can not have solution for ex2 and ex1. Since ex 1 + ex2 = 120-72 = 48 and ex1 + 2ex2 = 247-3*72 = 31. In this set of equation no solution exists for ex1 and ex2. How i solved was subtract both equations to get following equation ex2 + 2ex3 = 147. From this ex3's max value is 63 only. Not 72. Please correct me if i am wrong. Thanks.
@GMATNinjaTutoring
Жыл бұрын
Interesting solution path! It's not quite giving you the right answer though, and I think that's because you're omitting the possibility that a location introduces ZERO items. The question doesn't rule out that possibility. So it's very possible for 72 locations to introduce all 3 items. In that case, we can't possibly know exactly how many locations introduced 0, 1, or 2 items -- but we also don't really care, since the question is only concerned with the minimum and maximum number of locations that offer all 3 items. :) I hope that helps a bit!
@ruchitajoshi3723
11 ай бұрын
Hi this is not working for the following sum In a group of 68 students, each student is registered for at least one of three classes - History, Math and English. Twenty-five students are registered for History, twenty-five students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?
@GMATNinjaTutoring
11 ай бұрын
Hi! Could you please explain what you mean when you say 'this is not working' for this question? Using the method Charles demonstrated in the video in question 3, I get an answer of 10 students registered for exactly two classes. If you get a different answer, could you please explain how you answered the question and I'll do what I can to help figure out where things are going wrong. Thank you!
@U_lingo
9 ай бұрын
in Q 8 , when I was doing tryin to be in time it felt like something I would never be able to do IN MY LIFE, but when took a breath an forgot about time I did it in like 30 seconds, is it natural? it's as if my mind stops working under time pressure. is everybody else like me? HELP PLEASE!
@GMATNinjaTutoring
8 ай бұрын
Great question! First, what you're describing is highly common and totally normal. Nearly every GMAT student finds anxiety interfering with their test-taking process at some point. While there's no silver bullet solution, what you describe is definitely the right track -- take a step back, reset your brain, and try diving back in with renewed focus. Some test takers find this issue actually gets worse on test day, and can have a big impact on their score. If you suspect that might be the case for you, you may want to check out our article on tackling test anxiety: www.gmatninja.com/gmat/articles/basics/how-to-tackle-gmat-anxiety I hope that helps!
@anujpatel4238
Жыл бұрын
Hey Charles, in the 6th question we essentially assume that the 2 events are dependent right? I came across a similar question on GMAT club where there was no such assumption and the answer was 0.7 (lower of the 2 probabilities of the X and Y)
@GMATNinjaTutoring
Жыл бұрын
Close! Q6 on the video doesn't say anything at all about whether the events are dependent or independent -- so based on the phrasing alone, it's possible that the two events are independent. Technically speaking, you don't need to assume that the events are dependent. Of course, if the events were actually independent, then the probability that both events occur would just be the product of the individual probabilities (0.7 * 0.85 = 0.595). In this case, that's not the correct answer, as explained in the video. So it turns out that the two events are dependent, not independent. But you don't need to assume that the events are dependent in the beginning -- you just need to recognize that the events COULD be dependent, and then reason through the question from there. The same is almost certainly true of the question you saw on GMAT Club. If the answer was the lower of the two probabilities, then the events were almost certainly dependent. Maybe the question didn't explicitly state any assumptions, but it probably doesn't need to -- generally speaking, it will be clear from the context whether the events are independent or dependent. Or in some cases (like Q6), it will be clear that either is fair game. Also, the GMAT doesn't really require you to have a perfect, technical understanding of independence vs. dependence. If you're familiar with those concepts, that's great. But it's not really a core part of the exam. I hope that helps a bit!
@HatinderpalSingh
Жыл бұрын
charles is so funny sometimes
@GMATNinjaTutoring
Жыл бұрын
He's kinda funny-looking, too. - Every other GMAT Ninja tutor
@user-fc2jd2jn4g
5 ай бұрын
i will get into graduate school. i appreciate your help
@HimanshuSharma-hq2ic
2 жыл бұрын
Hey Charles, In this video you mentioned that the number of questions (weightage) from this topic will be on the lower side ~3%. I am looking for similar insight on SC topics so that I can make sure I am spending more time on the right topics. Could you please redirect me to any existing resource on this please. Would also be great to see the topic weightage for quant overall.
@GMATNinjaTutoring
2 жыл бұрын
Thank you for the question, Himanshu! The data I cited in the video was from GMAT Club's autopsy of the two free, official mba.com practice tests. The data is available at these links: - gmatclub.com/forum/what-is-tested-on-the-gmat-344670.html#p2698641 - gmatclub.com/forum/hardest-verbal-questions-tested-on-the-gmat-prep-software-345076.html Take these with a HUGE grain of salt though, especially for verbal. GMAT and EA questions often span multiple topics, and while it's certainly nice to have a general sense of which topics are truly important, you don't want to take the numbers TOO literally. That's particularly true on sentence correction. Very, very few SC questions test just one concept. Meaning and logic are part of almost every question, and several different grammar/usage concepts often appear in any individual question. So while I enjoy the data that GMAT Club compiled, I'm not sure that it's terribly actionable for SC in particular. I hope that helps a bit!
@leonkarsten
Жыл бұрын
My head is still spinning
@GMATNinjaTutoring
Жыл бұрын
Mine never stops spinning. 🤷🏻♂
@abdur5908
Жыл бұрын
Question 7 , I made a 3 way matrix instead of a two way one and found that statement 1 was sufficient but statement 2 was not sufficient . Where did i go wrong ? Was so excited that i almost got one of the questions in the video by myself 😒
@GMATNinjaTutoring
Жыл бұрын
Unless we're watching you do the question, it's hard to know exactly why you missed the question. But as emphasized in the explanation in the video, it's very easy to misinterpret the question, especially if you're setting it up as a 3-way matrix. For most people, the key is recognizing that if a consumer "did not say that they approve of policy B", that's not the same thing as saying that they DISAPPROVE -- if they "did not say that they approve", they either disapproved or they're neutral. For more, check out the explanation starting at the 38:25 mark: kzitem.info/news/bejne/sKmBr2Frs2V8mmk. I hope that helps a bit!
@rudrakshsharma1066
Ай бұрын
question 8 was the most difficult and mind boggling for me 🥲
@GMATNinjaTutoring
Ай бұрын
Yup, it's a rough one! Don't lose any sleep over it at all -- as we get to the end of this particular videos, the questions get pretty nasty. They're a nice little workout if you're shooting for an elite quant score, but this is about as tough as things get on the GMAT. So there's no shame at all in struggling with those last few questions. Have fun studying, and thank you for watching!
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