Shake the hands
Probability
Level
2
At a party, everyone shook hands with everybody else. There were 66 handshakes. How many people were at the party?
The answer is 12.
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1 solution
For a party with N people in it, there will be ( ( N × ( N − 1 ) ) / 2 ) handshakes.
N ( N − 1 ) = 1 3 2 , so N = 1 2 .