Note We use this type of regrouping in a subtraction problem when the fraction in the second mixed number is larger than the fraction in the first mixed number. EXAMPLE 5 Subtract 11 2 5 4 3 4 . Solution To fi nd the difference 11 2 5 4 3 4 , we must fi rst write the fractional parts with a common denominator. The LCD of 2 5 and 3 4 is 20. 2 5 4 4 8 20 3 4 5 5 15 20 11 2 5 4 3 4 11 8 20 4 15 20 Write the fractions with the LCD. Can we perform the subtraction as it is written here? No! The second fraction is larger than the fi rst. Regroup (borrow) 1 from the whole-number part of the fi rst mixed number. 11 8 20 Write 11 as 10 1. 11 8 20 s 10 1 8 20 10 20 20 8 20 10 28 20 Now we can subtract. 11 2 5 4 3 4 11 Get a common denominator for 1 and 8 20 4 15 20 8 20 . Write the fractions with the LCD. Rewrite 11 8 20 as 10 28 20 . Subtract. 10 28 20 4 15 20 6 13 20 YOU TRY 5 Subtract 12 1 5 11 2 3 . www.mhhe.com/messersmith SECTION 4.5 Adding and Subtracting Mixed Numbers 261
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