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Austin Community College

Pre-Algebra: Lesson 045

Lesson Description

Students learn to subtract mixed numbers by first subtracting the fractions, then subtracting the whole numbers. For example, to subtract 6 1/3 - 4 2/3, first subtract 1/3 - 2/3. However, notice that 1/3 - 2/3 equals a negative fraction. In this situation, the first fraction, 6 1/3, can be rewritten as 5 + 1 1/3, or 5 + 4/3, or 5 4/3. Therefore, the original problem, 6 1/3 - 4 2/3, can be rewritten as 5 4/3 - 4 2/3. Now, subtract the fractions, 4/3 - 2/3, to get 2/3, and subtract the whole numbers, 5 - 4, to get 1. So 5 4/3 - 4 2/3 = 1 2/3. Note that some of the problems in this lesson also require the student to find a common denominator for the fractions. For example, 8 5/16 - 1 1/8.