Skip to content

Village wives and the public infidelity announcement

Question

In a village, each wife knows whether every other husband is unfaithful but not whether her own is, and a wife who deduces that her husband cheats evicts him the next morning. All wives are perfect logicians and hear everything announced publicly. A visitor publicly states that at least one husband is unfaithful. Nothing happens until the morning of day 1010, when the first evictions take place. How many husbands are thrown out?

Short answer

10. By induction, if there are kk cheaters, each of their wives sees k−1k-1 and waits to see whether those are evicted by day k−1k-1; when nothing happens she concludes her own husband cheats. So all kk evictions happen together on day kk, giving k=10k=10.

Adapted from Crack, Heard on the Street, Q1.33, p.16; question and answer rewritten by SelfMadeQuant.com.

See the hint and the full worked solution in the question bank (free account).

Open the worked solution