YOU TRY 3 Identify the least common denominator of 4 5 and 2 3 , then write each fraction as an equivalent fraction with the LCD as its denominator. For each group of fractions, identify the least common denominator, then write each fraction as an equivalent fraction with the LCD as its denominator. a) 7 9 and 2 3 b) 9 20 , 1 8 , and 3 5 Solution a) The LCD of 7 9 and 2 3 is the least common multiple of 9 and 3. The least common multiple of 9 and 3 is 9, so LCD 9 7 9 ? 9 and 2 3 ? 9 2 3 3 3 6 9 The LCD of 7 9 and 2 3 7 9 is already written with the LCD. is 9, so 2 3 6 9 and 7 9 remains the same. b) Use one of the methods of Section 4.2 to fi nd that the least common multiple of 20, 8, and 5 is 40. Therefore, LCD 40. Write each fraction with the LCD. 9 20 ? 40 1 8 ? 40 3 5 ? 40 9 20 2 2 18 40 1 8 5 5 5 40 3 5 8 8 24 40 The LCD of 9 20 , 1 8 , and 3 5 is 40. Then, 9 20 18 40 , 1 8 5 40 , and 3 5 24 40 . YOU TRY 4 For each group of fractions, identify the least common denominator, then write each fraction as an equivalent fraction with the LCD as its denominator. a) 5 8 and 9 16 b) 18 25 , 7 10 , and 1 20 If the denominators are large, a good way to fi nd their LCD is fi rst to make a list of the multiples of the largest denominator or to use prime factorization. EXAMPLE 4 You might need to use the previous methods for finding a LCM to find the LCD. 238 CHAPTER 4 Adding and Subtracting Fractions www.mhhe.com/messersmith
messersmith_power_basic_college_1e_ch4_7_10
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