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Quant skills

Moji asked on Sep 03, 2017 - 4 answers
Actively preparing for my first round McKinsey interviews.

Hi guys,

I have my first round McKinsey case interviews (Associate position) coming up at the end of the year. Postponed due to personal reasons -HR asked me to phone in again and book a suitable time later in the year and I am therefore using the time to practise as much as I can.

My problem is I really am not doing well with the quant calculations in terms of knowing the approach to use to solve the case (not framework - mathematical approach). When I look at the answers I ask myself why certain numbers were multiplied/divided as it would never have otherwise occured to me to perform the calculation in that particular method. Can ANYONE please please tell me if this problem is normal and how to go about it. I am beginning to get really discouraged. Ironically I got an A in Math in school (haha) but I cant seem to wrap my head around why some calculations were carried out using the math approach used in the cases(s).


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replied on Sep 03, 2017
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Hi Moji,

it seems your issue is not the math computation, but rather how to structure the math part once you receive a question (that is, the logic behind that you should apply). This means you should not work on your computation skills only, as this is not the reason for the problem. Based on my experience, there might be two reasons for struggling on the math approach, besides lack of computation skills:

  1. You cannot structure the approach due to excessive pressure. Some people can easily find the solution of a math problem when doing that quietly on their own, but are unable to do so once they receive time pressure (eg You have 5 seconds to give me the solution of this – what is 83% of 83?). In this case, I would suggest to cover the problem doing math exercises with a timer, so that you can test yourself with a specific time deadline.
  2. You lack business knowledge of what is the right way to perform math. For example, you don’t know what’s the formula for discount cash flow, price elasticity, etc. In this case, I would suggest to solve the problem reading a good amount of cases, which involves math. You can identify them taking some of the several consulting MBA handbooks online, skim them and stop and read the case when you see some math present. You can then review online the topic you found for further reference. This should give you quickly and for free the right knowledge you need for cases.

Hope this helps,


I think you are right on that Francesco. I've been very used to my medical science job that my math has gotten pretty rusty and as you guessed my background is pretty limited. From your experience - how much prep time should I give to get up to speed with the requirements for a first round interview? I've got roughly 10 weeks and wondering if it is even sufficient? — Moji on Sep 03, 2017

Anonymous replied on Sep 03, 2017

Hey Moji,

Congratulations on your 1st round McK.

Regarding the math - since you are already in the first round I'm assuming you went through the McK PST and also having a biomedical background (and having As in Math) I'm assuming math by itself is not the problem.

Usually in a math question during a case there are 3 important moments after understanding the question: (1) coming up with a strategy to solve the problem and communicating said strategy to the interviewer; (2) solving the problem and sharing it with the interviewer; (3) discussing what the result means to the case.

From your comment, I get the problem is in step (1). Now 2 things could be happening: (1) you solve the problem using a different strategy than what is shown in the solutions but reach to the same number (which is perfectly OK and you should not worry about it); and (2) you come to a different number which means your strategy is wrong.

Lets assume (2) is what happens because otherwise there isnt any problem here. There are (3) things you can do to improve your strategy math solving skills:

(1) Do exams similar to the McK PST: This will force you to solve similar type of questions;

(2) Get yourself familiar with all major financial terms and how they relate: this could be one of the sources of your problem since you said you dont know why certain numbers were being multiplied which could mean you dont know the relationship between certain numbers;

(3) Focus on heavy quant. cases in your preparation: As you said you have a couple of months left so by focusing on areas that you feel weak you will bring that area up with time.

Hope this helps!

Nuno you basically hit the nail on the head! That's exactly what is frustrating me. Not the math calculations but "how did they even use this method/strategy?" I'll start brushing up my basics and see how far I get. — Moji on Sep 03, 2017

Verena replied on Sep 03, 2017
Practicing for McKinsey and Bain interviews in September

Hi Moji,

Congrats to the McKinsey interviews! I just wanted to tell you that I, even though I have a very quantitative background, also struggled with the maths. What helped me is the extensive practice of the basic math skills with tricks that I saw on the tecmath youtube channel. Then you can use mental math apps or the math section here on preplounge to get better. Once you are more confident with the basics, I found, it is easier to apply it naturally in a business setting.

Good luck, and I am sure you'll do well with enough practice!


Thanks so much Verena! I'll definitely give it another stab. Hope you got through your interviews :) — Moji on Sep 03, 2017

replied on Sep 11, 2017
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Hi Moji,


Here is how you can improve your math skills. It requires some time so I would try to reschedule your interview and prepare accordingly:

1) Fast math - train, train, and train again

  • Learn how to multiply double digit numbers (google fast math tips)
  • Learn the division table up to 1/11 (i.e. 5/6 = 83.3)
  • Learn how to work with zeros (Hint: 4000000 = 4*10ˆ6)
  • Use math tools (Mimir math for iOS), Math tool on Viktor Cheng website to practice

2) Critical Reasoning

  • GMAT test CR and IR parts (Official guide and Manhattan prep)
  • Mckinsey practice tests
  • PST like tests from the web

3) Working with tables and graphs and deriving conclusions

  • Study "Say it with Charts" book
  • Check all available MBB presentations and publications. Practice to derive conclusions and check yourself with the actual ones from the article/presentation
  • GMAT IR part (Official guide and Manhattan prep)
  • Learn basic statistics (Any GMAT or MBA prep guides)

4) Case math

  • Practice common market sizing topics (Airport passenger flow, real estate volumes, subway passenger flows, car usage, etc.). You should become comfortable with making assumptions
  • Learn key financial topics (P&L and balance sheet and how to analyze them, Basic Valuation principles via NPV and comps) and case tips (e.g. Rule of 72, Perpetuity)

Good luck with your interviews!

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