Question

Everybody in a room shakes hands with everybody else. The total number of hand shakes is 66. The total number of persons in the room is 

A. 11  B. 12 C. 13 D. 14

Answer 1

B. 12

Formula:-

Let total time of handshakes=ⁿC₂ = 66

⇒n²-n=132

⇒(n-12) (n+11)=0

n=12 or n=-11