Everybody in a room shakes hands with everybody else. The total number of hand-shakes is 55. The total number of persons in the room is:

A 11

B 12

C 8

D 14

E None of these

Correct Answer: Option A

Let the total number of person be N

∵ Total number of hand-shakes is 55

∵ For a hand shake we require two people, total number of handshake is NC2

∴ ⁿC₂ = 55

∴ N = 11 persons