#math trivia #84 solution

Burt Kaliski Jr. (@modulomathy)
3/24/12 10:06 AM
#math trivia for #March24: #84 is 2^2*3*7. How many divisors does it have and why? Compare solution to #42: wp.me/p2ef3C-f

There are 12 divisors of 84: 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42 and 84.

Here’s why the number is 12: Each divisor must have the form 2^a*3^b*7^c where a is between 0 and 2, and b and c are 0 or 1. There are 3*2*2 = 12 possible combinations of the three exponents.

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