12 members were present at a board meeting. Each member shook hands with all of the other members before & after the meeting. How many handshakes were there?
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Think of it this way: the first person shakes hands with 11 people, the second person also shakes hands with 11 people, but you only count 10, because the hand shake with the first person was already counted. Then add 9 for the third person, 8 for the fourth, & so on. 66 handshakes took place before & 66 after the meeting, for a total of 132.