Math Problem of the Week #10

15 friends meet together for a party. Each friend shakes the hand of each other friend, not counting his own. How many handshakes were there in all?

 

BONUS QUESTION: In a similar situation, there are x friends meeting together for a party. Each friend shakes the hand of each other friend, same as above. There were 231 handshakes. How many friends were at the party?

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