At a family reunion, every adult shakes hands with every other adult exactly once. If there are 45 handshakes in total, how many adults are at the reunion?
10
The formula for handshakes among n people is n(n-1)/2 = 45. Solving this gives n(n-1) = 90. The consecutive integers whose product is 90 are 10 and 9, so n = 10.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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