Page 30 - MarceAlgebra Demystified

CHAPTER 1 Fractions 17

119 17 119 7 17 6 833 102 935
9: þ ¼ þ ¼ þ ¼
180 210 180 7 210 6 1260 1260 1260
187
¼
252

Adding More than Two Fractions

Finding the LCD for three or more fractions is pretty much the same as
finding the LCD for two fractions. Factor each denominator into its
prime factorization and list the primes that appear in each. Divide the
LCD by each denominator. Multiply each fraction by this number over
itself.

Examples

4 7 9
þ þ
5 15 20
Prime factorization of the denominators: 5 ¼ 5
15 ¼ 3 5
20 ¼ 2 2 5
The LCD ¼ 2 2 3 5 ¼ 60
4 7 9 4 12 7 4 9 3 48 28 27 103
þ þ ¼ þ þ ¼ þ þ ¼
5 15 20 5 12 15 4 20 3 60 60 60 60

3 5 1
þ þ
10 12 18
Prime factorization of the denominators: 10 ¼ 2 5
12 ¼ 2 2 3
18 ¼ 2 3 3
LCD ¼ 2 2 3 3 5 ¼ 180
3 5 1 3 18 5 15 1 10 54 75
þ þ ¼ þ þ ¼ þ
10 12 18 10 18 12 15 18 10 180 180
10 139
þ ¼
180 180