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Can writing out calculations slow you down when taking PST and gmat style tests?

Patrick asked on Sep 11, 2018 - 3 answers
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Guennael replied on Sep 12, 2018
Ex-MBB, Experienced Hire; I will teach you not only the how, but also the why of case interviews

Can writing out calculations slow you down? Well, yes - of course! What will happen if you don't write it down however? Can you do the math in your head (or estimate it)? If so, don't write things down. If you can't, then you really only have two options: (1) your write the math down, "waste" a little bit of time, and have a chance to get to the right answer, or (2) you don't write it down, get the wrong answer, and never even get a chance to get an interview.

What you want to do it practice quick math enough that you have time to finish the whole test within the allocated time and with sufficient accuracy that your score helps you rather than hurts you. PrepLounge has good material, caseinterviewmath.com is a fantastic resource, and you will also find dozens of books on the suject at your local library, Barnes & Noble or Amazon. There's no shortcut, you will have to put in the work sorry.

Patrick updated his answer on Sep 12, 2018

Hi, thank you both for taking the time to answer this for me. It has really helped me. Patrick


Vlad replied on Sep 12, 2018
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School


I think the answer is in your question already. Here is how you can progress with mental / written math:

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

2) Learn how to work with zeros. You've mentioned - always use 10^power instead of zeros


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

Finally - practice a lot with the math tools (Preplounge, V. Cheng, Mimir Math)

Good luck!

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