What Is Left

A pie is cut up at lunch. Tom eats 1/2 of the pie and Sara eats 1/6 of the whole pie. What fraction is left? The whole pie is 1, so start from 1 and take both pieces away. Use r for the rest: r = 1 - 1/2 - 1/6.

Now work it as any subtraction of fractions: write 1 as 6/6 and use the common denominator 6, which gives r = 6/6 - 3/6 - 1/6, then r = 2/6, and in lowest terms r = 1/3. One third of the pie is left.

Read the story closely. Here both pieces are fractions of the whole pie, so both come off the 1. If a story says someone eats 1/6 of what is left, that piece is a fraction of a smaller amount, and the calculation is different.