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# Are there any math Short-Cuts for the quantitative Section?

case math
New answer on Jan 23, 2020
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I am still struggling with calculating efficiently.

• North America: 23 employees * 8 hours a day * 220 days a year * (1,4 * 25 EUR/hour) = EUR 1,416.800

Are there any shortcuts to this calculation or do I just have to get quicker with my pen&paper math (long multiplications). Even if I summarize the calculation to 23 * 1760 * 35, I feel that I still need long multiplication to solve it.

Do I miss the obvious here? Or is long multiplication indeed intended for this calculation?

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With multiple-factor multiplications like these it is often a good idea to change the order of operations and group the numbers more efficiently.

As a first step, I would propose the following:

((25 * 8) * 1.4) * 220 * 23 = (200*1.4) * 220 * 23 = 280 * 220 * 23

As a second step, the 280 * 220 can be simplified using the distance-of-squares method. Both numbers are 30 away from 250, so you can calculate the result as follows:

280 * 220 = 250^2 - 30^2 = 62500 - 900 = 61600

Please note that there is a shortcut for squares ending in 5 that I've used here - basically, if you square a number ending in 5, take the non-unit digit, multiply it with itself + 10, and add 25.

And now the calculation boils down to 61600 * 23, which I would treat as such:

61600 * 23 = 61600 * 20 + 61600 * 3 = 1232000 + 184800 = 1416800

Hope this helps!

Hello!

I would:

• 1st: write the whole equation, just as you did in the post
• 2nd: try to re-arrange it in a way in which you find easy relationships among numers (when possible) -e.g., 8*25 is 200, which multiplied per 220 is raughly 200 squared, etc.) This for sure depends on if you are allowed to round up numbers or not, which is something you should clarify with the interviewer)

Hope it helps!

Cheers,

Clara

Hi,

I recommend this video to learn how to multiply double-digit numbers really fast. In my opinion it's the biggest contributor to the speed of calculations:

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

Best