Get Active in Our Amazing Community of Over 458,000 Peers!

Schedule mock interviews on the Meeting Board, join the latest community discussions in our Consulting Q&A and find like-minded Case Partners to connect and practice with!

Hi all - does anyone have any material to prep mental maths? Thanks a lot!

Case Calculations case interview preparation case math McKinsey mental math Online Tests
New answer on Nov 10, 2020
17 Answers
28.4 k Views
Anonymous asked on Jan 19, 2018

Overview of answers

Upvotes
  • Upvotes
  • Date ascending
  • Date descending
Best answer
Anonymous replied on Jan 19, 2018

There are many sources u can use e.g.

1. Mental Maths Tool from Preplounge

2. Mental Maths Tool from Victor Cheng

3. GMAT Questions

4. IQ Test also include mental maths questions e.g. solving basic equations

But for basic mental maths the tool on PL and the tool of VC are sufficient. Besides of this u should also make sure that u know how to solve more complicated caluculations on a piece of paper. Good luck with ur prep.

Was this answer helpful?
10
Vlad
Expert
replied on Jan 19, 2018
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School

Hi,

Basically, you need to develop 3 calculation skills:

1) Learn how to multiply double digit numbers (google fast math tips or The Veda math).

2) Learn how to work with zeros. Best way - always use 10^power instead of zeros

Example:

300x9000 = 3*10ˆ2 x 9*10ˆ3=3x9*10ˆ(2+3)=27*10ˆ5

Handwritten it looks not that complicated. If you get used to writing all the numbers that way, you will never loose zeros and all multiplications/divisions will be replaced with + or -.

3) Use math tools (Mimir math for iOS, Math tool on Viktor Cheng website) to practice. Train, train, and train again

PS, Additionally I suggest to learn how to make the division mentally:

4) Learn the division table up to 1/11 (i.e. 5/6 = 83.3%). It will help you calculate any percentage problems

Good luck!

Was this answer helpful?
John on Jan 19, 2018

Where can one find a division table with the decimals ? The classic one is only the obvious numbers.

Vlad on Jan 20, 2018

You can make it yourself with a calculator;)

Francesco
Expert
Content Creator
replied on Jan 20, 2018
#1 Coach for Sessions (4.500+) | 1.500+ 5-Star Reviews | Proven Success (➡ interviewoffers.com) | Ex BCG | 10Y+ Coaching

Hi Tiago,

I agree with Alexander, Vlad and Tania; I would also suggest you to:

  1. Write down the initial formula for the math computation. That’s not always feasible when you have to do mental math, but if possible try to always do so. I found many candidates start to do math without having clear what is the overall formula they have to use. This can lead to longer computations and therefore mistakes. Eg say you have to find the additional revenues from a new technology that increase revenues by 13% per employee. You have 180 employees. Current revenue per employee per month in this division is €1200. You want to find the annual increase in revenues.
    1. Option 1 (average): Compute current revenues per year (180*12*1200); then compute new revenues per year (180*12*1200*1,13). Then subtract.
    2. Option 2 (great): Write down the formula from the beginning. You can immediately spot you can aggregate the formula as (0,13*180*12*1200). You avoid a full computation that could lead to mistakes and appear faster in front of the interview at the same time
  2. Train math under pressure. Most of the mistakes done in math during the interview are not due to lack of math knowledge. Rather, to the fact that you have to do math under pressure and are not used to that. That’s actually what you should train for. Best thing would be to do math with a timer, setting it with a challenging constraint that will force you to train under pressure. Eg if you can do percentage exercises in 15 seconds each on average, train with a timer set at 12-13 secs. The fact and feeling you don’t have enough time will help you to train for pressure.

Best,

Francesco

Was this answer helpful?
Guillaume replied on Jan 20, 2018

The only book you need is "Secrets of Mental Math" by Arthur Benjamin and Michael Shermer, for few bucks on Amazon.

Easy to "read", training pages, super useful tricks for cases and for your whole life : I don't understand why calculation is not tought like that at school...

Was this answer helpful?
2
Tania replied on Jan 19, 2018
Experienced consultant looking for case partners to practice with - tjorge@live.com.au
Was this answer helpful?
2
Gaurav
Expert
Content Creator
replied on Nov 10, 2020
#1 MBB Coach(Placed 750+ in MBBs & 1250+ in Tier2)| The Only 360 coach(Ex-McKinsey + Certified Coach + Active recruiter)

For practicing and improving your mental math you can find also some apps and tools, besides Victor Cheng’s math tool (Magoosh's mental maths app, Mental math cards challenge app etc). But there are some facts that will help in overall improvements:

Consulting math is very different from academic math. Working consultants - and consulting interview candidates - are always under time pressure. Results are what matter and answers are required simply to be good enough to guide business decisions, rather than being absolutely correct. The next important thing is that rather make it on the paper to structure the notes and then to communicate the results clearly rather than make your calculations fast

The time pressure in case interviews is severe and you cannot afford to waste time. But to make your calculations right you shouldn’t be in a rush. So, I would recommend you here to work on both - practice with time limitations and learn how to keep your mind peaceful and concentrated (it might be not so popular advice here, but mediations really make their job here ). Be comfortable and confident to state your answers not as a questions. Interviewers notice this, and this will not give a credit. If you need any further help or career advice, feel free to reach me out.

And here is math app for practicing math fractions and percentages from one of PL participant https://apps.apple.com/us/app/case-math/id1507653375?mt=8&ign-mpt=uo%3D4

Also, there is a tool provided by PrepLounge (https://www.preplounge.com/en/mental-math.php

Does it make sense to you?

GB

Was this answer helpful?
Clara
Expert
Content Creator
replied on Sep 30, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

I would strongly recomment you practice it with the Integrated Reasoning part of the GMAT exam.

There are free exams in the internet that you can use for practice (the one of LBS MBA page, Verits prep, as well as some free trials for courses such as the one of The Economist (https://gmat.economist.com/)

Hope it helps!

Cheers,

Clara

Was this answer helpful?
Anonymous replied on Jul 08, 2020

Dear A,

For practicing and improving your mental math you can find also some apps and tools, besides Victor Cheng’s math tool (Magoosh's mental maths app, Mental math cards challenge app etc). But there are some facts that will help in overall improvements:

Consulting math is a very different than academic math. Working consultants - and consulting interview candidates - are always under time pressure. Results are what matter and answers are required simply to be good enough to guide business decisions, rather than being absolutely correct.

The next important thing is that rather make it on the paper to structure the notes and then to communicate the results clearly rather than make your calculations fast

The time pressure in case interviews is severe and you cannot afford to waste time. But to make your calculations right you shouldn’t be in a rush. So, I would recommend you here to work on both - practice with time limitations and learn how to keep your mind peaceful and concentrated (it might be not so popular advice here, but mediations really make their job here ).

Be comfortable and confident to state your answers not as a questions. Interviewers notice this, and this will not give a credit.

If you need any further help or career advice, feel free to reach me out.

Best,

André

Was this answer helpful?
0
How likely are you to recommend us to a friend or fellow student?
0 = Not likely
10 = Very likely
You are a true consultant! Thank you for consulting us on how to make PrepLounge even better!
^