ABSTRACT
This chapter uses only the very elementary idea that an experiment with few possible outcomes cannot distinguish between many possibilities. For example, suppose there are 14 coins of which one is counterfeit and weighs either more or less than the others. Can one find the counterfeit, and determine whether it is light or heavy, using only three weighings with a balance scale? In fact, no: the number of possible outcomes of the weighings is at most 3x3x3 = 27 and there are 28 possibilities one is asked to distinguish. In the first puzzle, this question is asked but for only 12 coins; the information constraint guides the reader to a solution. In the remaining 10 puzzles, information is considered in a variety of ways; finally the theorem introduces the reader to the basics of cryptography.
