Wednesday, August 10, 2005

Maths is fun

Rex Hubbard writes:
Try to solve this problem mentally and in less than six steps.

(5^6) - 1 is divisible by:

A) 58
B) 59
C) 61
D) 62
E) 86

I find that solving math problems can be surprisingly satisfying. I'll put my solution in the comments, in case any readers want to try it for themselves first.


  1. The difference of two squares:
    5^6 - 1 = (5^3 - 1)(5^3 + 1)

    Left hand factor = 124 = 62 * 2

    Thus the answer is "D".

  2. How long did this take you? I came to the same conclusion in about 2mins.

  3. Yeah, around a minute, I think.


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