Question

At a conference, 12 members shook hands with each other before & after the meeting. How many total number of hand shakes occurred?​

Answer 1

Correct answer: 132

Explanation: The first person shook hands with 11 remaining people, the second person also shook hands with 11 people, but we count 10, as the hand shake with the first person has already been counted. Then add 9 for the third person, 8 for the fourth one & proceeding in this fashion we get: 11 + 10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 66.

Hence 66 hand shakes took place before & 66 after the meeting, for a total of 132.

Answer 2

no.of person= 12

2 hands to meet..

by permutation and combination

= 12 C2

= 66