Definition/Procedure Example 4.4 Adding and Subtracting Unlike Fractions In order to add or subtract fractions, they must have a common denominator. Adding or Subtracting Unlike Fractions Step 1: Determine the least common denominator (LCD), and write it on your paper. Step 2: Rewrite each fraction with the LCD. Step 3: Add or subtract. Step 4: Write the answer in lowest terms. (p. 242) Add 4 9 5 6 . Step 1: Write down the LCD of 4 9 and 5 6 . LCD 18 Step 2: Rewrite each fraction with the LCD. 4 9 2 2 8 18 5 6 3 3 15 18 Step 3: Add. Equivalent fractions 4 5 8 15 9 6 18 18 8 15 18 23 18 or 1 5 18 Equivalent fractions Step 4: Ask yourself, “Are 23 18 and 1 5 18 in lowest terms?” Yes. We can write the answer as an improper fraction or mixed number. Add and Subtract Natural Numbers and Fractions We can add and subtract natural numbers and fractions by changing the natural number to an improper fraction fi rst. (This is a useful method in algebra.) (p. 249) Add or subtract by fi rst changing the natural number to an improper fraction. a) 3 5 8 b) 1 3 7 a) We can say that 3 5 8 3 5 8 . Or, we can rewrite 3 as a fraction with a denominator of 8. Rewrite with a denominator of 8. 3 5 8 3 1 5 8 24 8 5 8 29 8 Write 3 with a denominator of 1. b) Write 1 as a fraction with a denominator of 7. Rewrite with a denominator of 7. 1 3 7 1 1 3 7 7 7 3 7 4 7 Write 1 as 1 1 . Applications of Adding and Subtracting Fractions Many applications involve adding or subtracting fractions. (p. 250) A rectangular transom window is 7 8 yd long and 2 5 yd wide. Find the perimeter of the window. Step 1: Read the problem carefully, and restate it in your own words. The length of a window is 7 8 yd, and the width is 2 5 yd. Find the perimeter of the window. 282 CHAPTER 4 Adding and Subtracting Fractions www.mhhe.com/messersmith
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