Posted by donna on Thursday, April 22, 2010 at 10:56pm.
for n people there will be C(n,2) handshakes
C(n,2) = 105
n!/(2!(n-2)!) = 105
n(n-1)/2 = 105
n^2 - n - 210 = 0
(n-15(n+14) = 0
n = 15 or n=-14, but n > 0
so there were 15 people
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