Fractions Drive One To....
Spring vacation was near and the teacher was trying to give her class an impression of fractions which would last until school resumed. She told them they could think of fractions at home as well as in school and gave such examples as "half a sandwich," "a quarter of a pie," and "tenth of a dollar."
At that point one little boy caught on and proudly contributed, "My father came home last night with a fifth."
Source: J. Braude's Handbook of Humor for All Occasions, 1958, p. 24