209.Handshakes Among Four Couples
★★★combinatoricsCh. 1 — Classical Probability and Combinatorics444+ Problems in Probability
A room of four couples greet each other by shaking hands. If each person shakes the hand of every other person besides their partner, how many handshakes occur?
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Count all possible handshakes among 8 people, then remove the ones that don't happen.
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