Question

there are 5 people at a party. each person must shake hands once with every other person at the party. how many handshakes does it take to do this?

Answer 1

Here's why: 

Say the 5 people are A, B, C, D, E 

A shakes hands w/ B C D E 
B shakes w/ C D E 
C with D E 
D with E 

That's 10