Edmund's Brainteasers
Problem 8
Problem 8: Weighing candles
The Church orders a box of 80 identical candles. The day after the box arrives they receive a message from the supplier saying that in error one of the eighty candles was made of a lighter wax which does not meet EU standards and the faulty candle must be returned. The Church has an old-fashioned balance (what else would you expect!) which determines how items placed on one side compare in weight with items placed on the other side (i.e. whether the two sides balance or one is heavier than the other). What is the least number of weighings necessary to find the one candle which is lighter than the rest?