I got asked these 2 Mental Math Questions during a M&A Interview, how do I actually solve them in my head?
Today I had my first ib interview which went pretty well until these 2 brainteasers came up and showed my lack of mental math skills:
What is 3 to the power of 12 What is 5 to the power of 5.
No way I could do these in my head
3^(2* 6)=9^(2* 3)=81^3= approx 80^3=6400*80=Approx > 512000
25* 25* 5=625*5=3125
So when somthing like 3 to the power of 12 comes up, I basically am not expected to calculate the exact number but rather approximate? Thank you!
I mean I wouldn't know how to do 81* 81* 81 in my head, just saying what I would say in an interview
Math major here. I always try this approach when I do those numbers in my head:
3^12 = (3^4)^3. Now 3^4 is 81, and you want 81^3. 81^3 = 81 * 81 * 81 = (80+1) * (80+1) * (80+1) In your head, it not hard to do (80 + 1) * (80 + 1) = 80^2 + 80 + 80 + 1 = 6561. The hard part is 6561 * 81. Try the same way above. 6561 * 81 = (6560 + 1) * (80 + 1) = 6560 * 80 + 6560 + 80 + 1. Now 6560 * 80, do 656 * 8 first. then put two 00s there. Then do the sum.
5^5 is easier. 25 ^ 2 = 625, 625 * 5 = 3125. Maybe I cheated, because as a Math major we are kinda supposed to know this one.
Hope this helps.
I am being honest here. I wouldn't be able to pull this off in my head without confusing the numbers
Alright. How did u answer the question during the interview?
http://arithmetic.lemo.education/ and learn. Mental math is an absolut classic in finance interviews, so just learn it. No big deal about it.
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