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Best resources for math improvement? (for a complete number novice!)

Anonymous A asked on Aug 22, 2019 - 2 answers

Whilst the preparation for case studies is going okay, I hit huge hurdles when I hit numbers.

I am looking for resources that will help me start from the very basics when it comes to mental math.

I have come across Victor Cheng's course (though his 'ultimate' option is way out of my budget!) and FastMath course. Does anybody have any reviews or recommendations on courses to take to improve mental math, please?

Thank you in advance!

Hi, can I send you a message about this? I have something to discuss on the topic — Jim on Aug 22, 2019

Have messaged you! — Anonymous A on Aug 22, 2019

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replied on Aug 22, 2019
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School
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Basically, you need to develop 3 calculation skills:

1) Learn how to multiply double-digit numbers (

2) Learn how to work with zeros. Best way - 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. For example, if your market is $620M and your revenues are $51M you can use 5/6 as a proxy to calculate the market share

Good luck!

Thank you! Do you have any opinions or experiences on the Fast Math course, or Victor Chen's Mental Math Fast course? — Anonymous A on Aug 22, 2019

What is the division table? Do you have any links that teach this? — Anonymous B on Aug 22, 2019

updated his answer on Oct 21, 2019
Former BCG | Case author for efellows book | Experience in 6 consultancies (Stern Stewart, Capgemini, KPMG, VW Con., Horvath, zeb)
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Hi Anonym,

for many who have difficulty with mental arithmetic, it's just the stressful interview situation. What about you? How good are you at mental arithmetic if you practice alone at home?

If it's just nervousness, I would recommend you practice the interview situation as often as possible (e.g. with friends or on Preplounge).

If it's the mental arithmetic itself, you can practice very well here:
If there is no other way, you can also do the calculations in writing on paper. However, I wouldn't advise you to memorize any multiplication tables.

If you have further questions, please contact me!

Best regards


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