GMAT Ninja Quant Ep 16: Combinations & Permutations

Do combinations and permutations questions on the GMAT or Executive Assessment keep you up at night? Do you struggle to figure out whether a question is a combination question or a permutation question? Do the formulas leave you in a muddle?

Alternatively, are you aiming for an 85+ in the quant section? Do you want to make sure you've left no stone unturned in your preparation?

In this video, Charles -- a veteran GMAT tutor with a perfect 800 score on the exam -- will help you develop a deep, intuitive understanding of combinations and permutations questions on the GMAT and EA.

The questions featured in this video will be gentle in the first half and tough in the second. The focus in the first half will be on your conceptual understanding. In the second half, Charles will dig into the variations the GMAT or EA could throw at you to make a combinations or permutations questions difficult.

This is video #16 in our series of full-length GMAT quant lessons. For updates on upcoming videos, please subscribe!

This video will cover:
➡️ Does order matter?
➡️ Intuition is more important than formulas
➡️ The basics you’ll need for an 80+
➡️ Hard questions (of dubious value)

This video is for you if:
➡️ You don't want to over study
➡️ Combinations and permutations keep you awake at night
➡️ You don't. know which formulas to use
➡️ You want a Q85+

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Want more GMAT test-prep tips and advice?

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Chapters:
00:00 Introduction
02:09 Q1 - Permutations Warmup
06:30 Q2 - Combinations Warmup
13:19 Q3 - At least one
19:40 Q4 - Digits Part I
25:54 Q5 - Only one from each
31:15 Q6 - Digits Part II
38:08 Q7 - One Digit Different

[DS-pgwh]

Dear GMAT Ninja Team, over the last two weeks I went through all of your 18 GMAT Quant Videos. I want to say a big thank you to the whole Team; you did an awesome Job!
I decided to watch your videos, because the Quant section really messed up my GMAT Test Practice scores. I don´t know yet whether the videos helped me to improve my score, but I definitely know, that I learned a lot and got to view a ton of questions from a different angle. Thus, for me it was absolutely worth putting the time in the course!
Again, thank you so much!!!
All the best for you guys!

[tunefunds]

On question 4, why do we not also divide by a further factor of 2 for cases in which N, N appear next to each other (that is to say, one N is somewhere else in the string of six letters but the other two N's are next to each other)? Thank you for making this tutorial, very helpful.

[PARItosh]

You are a SAVIOUR Charles <3 . I was super scared of these P and C questions. Just one doubt though, should we expect distribution problems in GMAT exam if we are targeting for a Q85+ score ?

[diegogreco]

Hey Charles, love the videos! I wanted to ask if, for mental clarity, it would be correct to define Combinations as operations where order DOESN'T matter (and therefore we use the formula), and Permutations as operations where order DOES matter (and we use the "slots" technique)... thanks for the help!

[kevinphilip]

The way I did q7 was I knew that 4000 would be excluded from the final answer, so I looked in the answers for any set of numbers that was 1 minus the other, in this case 215 and 216 😅

[Ibragim-dpow]

Hi, I just want to clarify something regarding the last question. You mentioned that for the digit 7, the same digits can be formed in 9 different ways because there are 10 digits. When we exclude 7, we are left with 9 options.

When 7 is in the thousands place, it includes 0 as a valid digit, resulting in 9 ways. However, when 7 is in the middle or at the end, does it not count if 0 is included? If 0 starts the number, it would become a 3-digit number.

Shouldn't it be 8 ways then? Specifically, there are 9 ways when 7 is at the beginning, and 8 ways when 7 is not at the beginning (providing we’re excluding 0). That would give us 8 × 3 = 24, in total 24 + 9 = 33 ways for just the digit 7. Am I wrong?🤔

[matthewgalloway]

Rocky Mountain Oysters joke @29:48 was absolutely hilarious. Thanks for making this video so fun and helpful.

[SwordSaint]

For q5, how do you proceed after selecting with 3 from a group of 15 ? you said we could work with that method also . Can you pls elaborate ? thanks in advance charles !

[shalinimaurya]

Need a video on remainder concepts of number system, thanks for awesome videos❤

[LakshmananMeyyappan]

For Q5, I thought of it as 15*12*9/3!. Got 270 as the answer, but not sure if its the right thought process

[amanuttam]

Hey Charles @GMAT Ninja Tutoring! for Q5 i used the logic of there being 15 people to choose from and once a person is chosen there cant be a repeat from that country, so first choice we have 15, then 12, then 9. I did 15 x 12 x 9 and then divided by 3! as its a combinations question. I also landed at the correct answer- does that approach make sense or is it just coincidence?

Thanks so much!

Aman

[cashivanggarg]

Hey Charles,
Firstly, like a billion thanks to you and your team for all the effort. And the Rocky joke was hilarious.
Just a teensy bit query, for Q5 i figured that answer must be a multiple of 15. And surprisingly there were just two. 2730 couldn't be the answer for obvious reason and got 270 as the answer. Is this approach advisable? It does save time and effort.
TIA

[jemimamanuel]

Hello, for q4, how do we get a factor of 6? Thanks much

[Sonshimishra]

if order didnt matter in 1st question, how to approach?

[ayushbahri]

Hi @gmatninja and Charles! Your videos have helped me a lot so thanks for that :D. I have a quick question though, you mentioned at the start that a Q75 to Q80 is a good score for modest goals but that would translate to 32% and 64% percentile respectively which would most likely lead to a score of a low to mid 500's on the GMAT focus (550-600 old one). Did you by any chance mean 75-80 percentile? Asking this because I have been stuck on a low Quant score even though I understand most of the concepts well. Thanks in advance!

[athuls]

Could solve the last question under 2 minutes 🎉