Question

I already know that the answer is 190 but why

Answer 1

You know that the total number of persons is 20 , so every person shakes hands with 19 persons.. It then mean that, there are 20×19=380 handshakes. But by every handshake two persons are involved. Therefore, 380 is the result of double-counting, which gives 190 handshakes.

Explanation:

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