This problem is the best-known simple example of a knight-knave problem, in which you come to a fork in the road and you do not know which way to go. In one direction lies happiness, in the other, disaster.

This problem is the best-known simple example of a knight-knave problem, in which you come to a fork in the road and you do not know which way to go. In one direction lies happiness, in the other, disaster. Fortunately, there is a guide sitting at the fork to direct you; unfortunately, you do not know whether the guide is a knight (always tells the truth) or a knave (always lies). The challenge is to devise a single yes-no question that will tell you which way is happiness. A powerful tool, truth tables, gives you a technique for dealing with many problems of this type. This mathematically rich problem was prepared by the Ohio Resource Center to accompany the Mathematics Program Models for Ohio High Schools developed by the Ohio Department of Education. (author/sw)