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Posted - 12/01/2013 : 00:51:27 GMAT-the official guide, #169 If N is a positive integer and N(N) is divisible by 72, then the largest positive integer that must divide N is ? A) 6, B) 12, C) 24, D) 36, E) 48. Answer is B) 12. Text* Since N(N) is divisible by 72, N(N)= 72k for some positive integer k." My first thought was to set up 72=n(n)k. But this is wrong. It should be n(n)= 72k. Can you explain?
text: " Since n(n) = 72k then 72k is a perfect square. since 72k =2(2)(2)(3)(3)k then k= 2m(m) for some positive integer M in order for 72k to be a perfect square." I don't follow the idea that k=2m(m). text: n(n)= 72k==2(2)(2)(3)(3)(2m(m)," so it follows on to the conclusion of a set of integers that MUST divide N are 1,2,3,4,6,12.
I don't see that 6, and 12 are part of this answer set, though since I was stumped earlier, this last puzzle might be obvious.