Coin-weighing problems and similar puzzles are often used as simple examples for education or as tests for algorithms. Typical weighing tasks have some number of coins (or other items) that should all be identical, but where one (or more) is known to be heavier, lighter or simply different from the others (in the case of coins usually a counterfeit). The goal is usually to find the counterfeit(s) using as few weighings as possible.
Used in Chap. 11: page 155