Problem Solving (PS) | Re: In a certain conference, if all the n attendees shake hands 105 times,

Hi..

Ofcourse the Q should mention that each shake hands with others once.

So choosing 2 out of n is nC2=\(\frac{n!}{(n-2)!2!}=\frac{n*(n-1)*(n-2)!}{(n-2)!*2!}=\frac{n*(n-1)}{2}=105....\) ..
\(n(n-1)=210=2*3*5*7=3*5*2*7=15*14\) So n is 15
C
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