Adding and Subtracting Fractions

How to Add or Subtract Fractions the numerators 2) Keep the same denominator 3/6 + 2/6 = 5/6

Different Denominators What if the denominator is not the same?

What To Do: Make the denominators the same by finding the least common denominator. LCD =12 Least Common Denominator (LCD): the smallest number that both denominators can be divided into.

Quick Review: Equivalent Fractions Find an equivalent fraction by dividing the numerator and denominator: Find an equivalent fraction by multiplying the numerator and denominator: Find an equivalent fraction by simplifying: 10/15 = 2/3 (Divide by 5) 6/8 = 18/24 (Multiply by 3) 12/16 = 3/4

Least Common Denominator (LCD) 9/12 + 2/12 = 11/12 Change the fractions to equivalent fractions that have the same denominator. Fractions must have a common denominator in order to be added or subtracted. Try to change the fractions so they have the least (or smallest) common denominator, because it makes the calculations easier!

A Method for Finding the LCD Multiples of 6: 6, 12, 18, 24, 30… Multiples of 4: 4, 8, 12, 16, 20 … LCD = 12

3/6 + 3/8 = Example 1 12/24 + 9/24 = 3/6 + 3/8 = = 21/24 LCD = 24 3/6 + 3/8 = 12/24 + 9/24 = = 21/24 3/6 + 3/8 = Multiples of 8: 8, 16, 24, 32, 40 … Multiples of 6: 6, 12, 18, 24 … LCD = 24

Example 2 10/20 - 1/4 = 10/20 – 1/4 = 10/20 - 5/20 = = 5/20 LCD = 20 10/20 - 5/20 = = 5/20 10/20 – 1/4 = Multiples of 20: 20, 40, 60, 80, 100 … Multiples of 4: 4, 8, 12, 16, 20 … LCD = 20

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