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# 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
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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.

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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!

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

You can make it yourself with a calculator;)

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

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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...

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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

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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

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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

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