9780470458389

A well-known logical puzzle has 20coins, one of which is counterfeittoo light or too heavyand a balance to compare the weight of any two sets of coins (the balance can tip to the right, to the left, or be even). For a given value of n, we seek a procedure for finding the counterfeit coin in a minimum number of weighings. Sometimes one is told whether the counterfeit coin is too light or too heavy. If we are told that the fake coin is too light, how many weighings are needed for 20coins?