Math & Logic · Ages 12–15
Riddle #158
Ten people meet at a party, and every person shakes hands with every other person exactly once. How many handshakes take place?
You solved this one before
Answer: 45
Each of the 10 people shakes 9 other hands, giving 90 — but that counts every handshake once from each side, so the real total is 90 ÷ 2 = 45.