Least Common Denominator The Least Common Denominator (LCD) is the Least Common Multiple of two or more denominators. How to find the Least Common Denominator: Find the Greatest Common Factor of the denominators. Multiply the denominators together. Divide the product of the denominators by the Greatest Common Factor. Example: Find the LCD of 2/9 and 3/12 Determine the Greatest Common Factor of 9 and 12 which is 3 Either multiply the denominators and divide by the GCF (9*12=108, 108/3=36) OR - Divide one of the denominators by the GCF and multiply the quotient times the other denominator (9/3=3, 3*12=36) How to rename fractions and use the Least Common Denominator: Divide the LCD by one denominator. Multiply the numerator times this quotient. Repeat the process for the other fraction(s) Example: Add 2/9 + 3/12 LCD is 36 First fraction (2/9): 36/9 = 4, 4*2 = 8, first fraction is renamed as 8/36 Second fraction (3/12): 36/12 = 3, 3*3 = 9, second fraction is renamed as 9/36 It is possible to add or subtract fractions that have the same denominator 8/36 + 9/36 = 17/36 Return to Top

#### Rename the Fractions using the Least Common Denominator

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