Devising a plan. We have a plan when we know, or know at least in outline, which calculations, computation, or constructions we have to perform in order to obtain the unknown. The way from understanding the problem to conceiving a plan may be long and tortuous. In fact, the main achievement in the solution of a problem is to conceive the idea of a plan. This idea may emerge gradually. Or, after apparently unsuccessful trials and a period of hesitation, it may occur suddenly, in a flash, as a “bright idea.” The best that the teacher can do for the student is to procure foe him, by unobtrusive help, a bright idea. The questions and suggestions we are going to discuss tend to provoke such an idea.