Cross Products and ProportionsProportion: two ratios that are equal.

Cross Products: checks to see if ratio’s are proportional. Multiply opposite numerator and denominators together. If they equal , the ratio’s are proportional.

Proportions

36 =

24

Cross Product

36 =

24

3 4 ∙ = 6 2∙12 = 12

Are the following ratios Proportional?5

15 =13

5 3 ∙ = 15 1∙15 = 15

85 =

106

8 6 ∙ = 5 ∙1048 = 50

68 =

912

8 9 ∙ = 6 ∙1272 = 72

Yes No

Yes

69 =

46

6 6 ∙ = 9 4∙36 = 36

Yes

Proportions with a variableTo solve a proportion that contains a variable, you find the value that makes the equation true.

36 =

x4

Cross Product to solve

36 =

x4

3 4 ∙ = 6x12 = 6x

12 ÷ 6 = 6x ÷ 62 = x

Solve each proportion3x =

26

3 6 ∙ = 2x18 = 2x

1012 =

x6

18 ÷ 2 = 2x ÷ 29 = x

10 6 ∙ = 12x60 = 12x

60 ÷ 12 = 12x÷125 = x