Question 127037
19C2 = 19*18/1*2 = 19*9 = 171
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You can see this pattern if you try it with 
2 people = 2C2 = 1 handshake
3 people = 3C2 = 3 handshakes
4 people = 4C2 = 6 handshakes
5 people = 5C2 = 10handshakes
etc.
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Cheers,
Stan H.