Consider a group of 20 people. If everyone shakes hands with everyone else, how many handshakes take place? thanks
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Originally Posted by mauro21pl Consider a group of 20 people. If everyone shakes hands with everyone else, how many handshakes take place? thanks That is number of combinations possible with 2 people out of 20. $\displaystyle {{20}\choose 2}=\frac{20\cdot 19}{2}$
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