© 2010 Pearson Prentice Hall. All rights reserved The Least Common Denominator and Creating Equivalent Fractions § 2.6.

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© 2010 Pearson Prentice Hall. All rights reserved The Least Common Denominator and Creating Equivalent Fractions § 2.6

Tobey & Slater, Basic College Mathematics, 6e2 A multiples of a number are the products of that number and the numbers 1, 2, 3, 4, 5, … The multiples of 3 are 3, 6, 9, 12, 15, … 3  1 3  2 3  3 The least common multiple, or LCM, of two natural numbers is the smallest number that is a multiple of both. Least Common Multiple (LCM)

Tobey & Slater, Basic College Mathematics, 6e3 Least Common Multiple (LCM) Example: Find the LCM of 4 and 6. The multiples of 4 are 4, 8, 12, 16, 20, 24 … The multiples of 6 are 6, 12, 18, 24, 30, 36 … The first number that appears on both lists is the LCM. 12 is the least common multiple of 4 and 6.

Tobey & Slater, Basic College Mathematics, 6e4 Least Common Denominator (LCD) A least common denominator (LCD) of two or more fractions is the smallest number that can be divided evenly by each of the fractions’ denominators. Since 4 can be divided into 12, the LCD of is 12.

Tobey & Slater, Basic College Mathematics, 6e5 Least Common Denominator (LCD) 20 is also the smallest number that can be divided by 4 and 5 without a remainder. Example: Find the LCD for 4  5 = 20 The LCD of is 20.

Tobey & Slater, Basic College Mathematics, 6e6 Finding the Least Common Denominator Three-Step Procedure for Finding the LCD 1.Write each denominator as the product of prime factors. 2.List all the prime factors that appear in either product. 3.Form a product of those prime factors, using each factor the greatest number of times it appears in any one denominator. Example: Find the LCD for 2  2  32  3  5 Product of primes Prime factors in either product: 2  2  3  5 The LCD is 60.

Tobey & Slater, Basic College Mathematics, 6e7 Creating Equivalent Fractions Fractions with unlike denominators cannot be added. To change the denominators and make them the same, 1) find the LCD and 2) build up the addends into equivalent fractions that have the LCD as the denominator. The LCD is 20. The building fraction property

Tobey & Slater, Basic College Mathematics, 6e8 Building Fraction Property For whole numbers a, b, and c where b  0, c  0, Example: Build to an equivalent fraction with a LCD of 20.