Sunday Times Teaser 2500 – No Title
by Peter Harrison
Published August 22 2010 (link)
A well-known puzzle asks: “If among 12 snooker balls one is a different weight, how can the rogue ball be identified — together with deciding whether it is heavier or lighter — in three weighings on a balance?”
Recently I faced a very similar problem of finding a rogue ball among a consignment of 39 identical- looking balls — and deciding if it was heavier or lighter. I had at my disposal a two-pan balance.
How many weighings did I need?