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Hi, what is the best way to brush up on quantitative skills for the Mckinsey PST and overall math calculations used during case interviews at Bain and Mckinsey? Thanks!

Anonymous A asked on Apr 06, 2018
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Francesco replied on Apr 06, 2018
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Hi Anonymous,

in general the best way to improve your math is to first identify your weak points, then work accordingly on them. That’s because “generally” prepare for math won’t optimize your preparation efforts. Rather, you should work on your identified weaknesses – in this way your preparation will be a lot more efficient.

For the PST I would suggest the following approach:

  1. Try to find at least 5-6 practice cases online. There are several you can find for free, if needed you can purchase some
  2. Do one of the tests immediately to check your score. As the passing score is around 70% and you have 26 questions, you should target a final score around 18
  3. Look at the type of questions you made more mistakes with. Understand if mistakes are due to math issues. If so, try to identify a pattern for that (eg you are slow in divisions/percentages; you did not use correctly elimination approach, etc). Work on them accordingly. Then proceed doing regularly the other tests before your interview.

For cases, you can follow an equivalent approach:

  1. Practice math-intensive cases, doing both live practice and screening MBA handbooks and focusing on the math heavy cases
  2. Write down all the mistakes you regularly do
  3. Understand which is the common pattern in your mistakes (most commons: missing zeros, wrong graph reading, unstructured communication of math steps). Remember that in live cases your communication of the math steps is also important - you should align with the interviewer on the steps to follow

Having said that, you are expected to know the following/have the following knowledge in a consulting interview:

  1. Good mental math. You can practice on some of the online tools available on daily base to improve. It is better if you allocate a small amount of time daily then practice intensively few days only before the interview
  2. Rule of 72 and difference between simple and compound interest
  3. Ratios from 1/2 to 1/10
  4. Breakeven formula
  5. DCF formulas and perpetuity (here there is a link to a complete analysis of them - https://www.preplounge.com/en/consulting-forum/case-net-present-value-calculations-325)

GMAT practice can definitely be useful as a way to speed up your math, but will help to focus on specific parts of math preparation only. If you have communication problems for your math or graph interpretation issues, for example, you wont be able to fix them with GMAT practice. On the other hand, live feedback from a good partner could help to understand what you are doing wrong and improve accordingly.

Best,
Francesco

Vlad replied on Apr 06, 2018
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Hi,

Here is how you can improve your math skills:

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

  • Learn how to multiply double digit numbers (https://www.youtube.com/watch?v=6ndkkPZYJHo)
  • 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 (for PST)

  • 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 math:

  • Interest rates calculations
  • Compound margin
  • NPV using the Rule of 72, Perperuity
  • CAGR using the Rule of 72
  • Currencies exchange calculations
  • Speed, time, distance calculations
  • Equations, systems of equations
  • Ratio & Proportions
  • Solving the problems by calculating the area of the triangle
  • Profit / breakeven formula
  • Correlations, outliers (being able to spot on the graphs, tables)

Good luck with your interviews!

Matthew
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replied on Feb 27, 2019
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There are a few articles in the BootCamp section:
https://www.preplounge.com/en/bootcamp.php/case-cracking-toolbox/practice-your-basics/why-math-matters

To summarize, you first want to be comfortalbe with the types of calcuations required in Case Interviews, on tthe types of Numbers you will encounter. The main point is that Case Numbers (the specific numbers involved in Case Interviews) have specific properties that you can use to simplify calcuations. They are usually "Round" nubmers with only a few significant digits (two or three significant digits). You're unlikely to need to mulptly numbers like 23,587 which has 5 significant digits. Make sure use practice problems that are reflective of actual CAse Numbers.

The basic operations you need to do in Case Interviews are additon, subtract, multiplicaiotn and division. Once you master these, you can move on to percetange calcuatoins, percetnage growth. You'll also need to know how compound growth works, but don't need to do accurate compound grwoth calcuations. Understanidng of CAGR and Rule of 72 is also important.

Once you have these skills, you'll need to apply them to Case Interview quant problems These can be quite complex, so make sure you practice a lot of these. Look for efficient solution methods for these problems rather than brute-force attacks.

Cameron
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replied on Apr 06, 2018
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Hi,

It's anything that covers basic non-verbal reasoning. I personally just practiced the most PST's on the McK website, but tests such as SHL online will also help

For case interviews, most people struggle with doing the maths whilst someone is watching. I would suggest trying practice cases with especially hard maths (ideally with a case partner), and it's pretty easy to make up some new maths questions to have a go at after you have seen a few cases.

Hope that helps!

Cameron

Andrea
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replied on Apr 06, 2018
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GMAT books (quantitative section) cover most of what you need in terms of math calculations. I personally always liked Kaplan, but worth to flip the pages of a few and then choose.

Hope it helps,

Andrea

Related BootCamp article(s)

How to Read Charts and Data in Case Interviews

We explain and give tips on how to understand and analyze graphs, charts and data presented by interviewer to candidates in case interviews.

Case Studies

The case study is the most important element of the case interview, which you'll have to nail in order to get into strategic consulting. Here you can learn the specific skills and concepts necessary to solve them.

Why Math matters

Your math skills will be tested in each and every consulting interview. So you better brush up mental math skills to succeed.

Interviewer-Led vs Candidate-Led cases

Case Interviews can be led by the candidate or by the interviewer: In Candidate-led cases the main challenge is the structure. In Interviewer-led cases the main challenge is to adapt quickly

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