SOLUTION: In a birthday party, each person shakes hand with every other person. If there was a total of 36 handshakes in the party, how many persons were present in the party?
If "n" is the number of persons, and if each shakes hand with every other person,
then the number of handshakes is .
So, you have this equation
= 36,
which gives
n*(n-1) = 2*36 = 72;
hence, n = 9.
ANSWER. There are 9 persons at the party.