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How to divide and multiple thousands, milions and bilions fast?

Jakub

Hello,

Does anybody have any tips/strategies on how to divide and multiple with K, M and B fast? I struggle a bit with adding the right amount of zeros to the result.

Examples could be something like 15B / 350 = .

K - thousand

M - milion

B - bilion

Thanks for tips!

Vlad replied on 07/07/2018
McKinsey / Accenture / Got all BIG3 offers / More than 300 real MBB cases / Harvard Business School

Hi,

There are several techniques that you can use:

1) 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 lose zeros and all multiplications/divisions will be replaced with + or -.

In your case, it will look like 63 * 10ˆ5 / 72 * 10ˆ2

2) Learn how to multiply double digit numbers

Pls check this video - https://www.youtube.com/watch?v=6ndkkPZYJHo It takes an hour to learn this method

3) Learn how to divide the numbers fast

If you need the precise calculation - you can use the basic division technique, calculating 630 / 72 * 10ˆ2 = 875

If you don't need it precise - Learn the division table up to 1/11 (i.e. 5/6 = 83.3%). It will help you calculate any percentage problems

In your case, it will be roughly 6/7 * 10ˆ3 = 85.7 * 10ˆ3 or 857. Since I know that it was the rough calculation and the real number should be bigger, I would round the final result to 870

Best!

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