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Case Math

Anonymous A asked on May 11, 2019

Hi,

in an interview I had to solve a problem, which ws conceptually easy, however, to get to total sales I had to solve this: 2*480*360*16*365*0.7

This is perfectly doable, but took me some time. How would you go about it in terms of simplifying and rounding?

Thanks!

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Vlad replied on May 12, 2019
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Hi,

4 skills might be used here:

  • Get used to round up and down (but ask the interviewer if that's ok)
  • Learn how to multiply double digit numbers (https://www.youtube.com/watch?v=6ndkkPZYJHo)
  • Learn the division table up to 1/11 (i.e. 5/6 = 83.3)
  • Get used to working with zeros using the powers of 10 (Hint: 4000000 = 4*10ˆ6)

Best!

Anonymous C replied on May 11, 2019

Round: 2 x 500(rounded up) x 400(rounded up) x 16 x 300(rounded down to compensate for previous roundings) x 0.7 = 1.34B. The precise answer is 1.41B, so it's within 10%.

Anonymous B replied on May 11, 2019

My guess is you need to estime the result rougthly and not go through hard computation. The idea here is to round the numbers

2*48*10*36*10*16*365*0.7 ~ 96*10*36*16*360*7 ~ 100*10*36*36*10*16*7 ~ 10^4*1296*112 ~ 10^5*1296*11~10^5*13*100*11~143*10^7. So rougthly speaking 1.4 billion

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