Day 58 Numeracy (Ratio and Proportion)

Ratio and Proportion

Ratio: A ratio is a comparison of two numbers

Ratios should be reduced into their lowest terms.

example: 20:5 should be written as 4:1

Proportion: A proportion is made up of two equal ratios

example: 20:5 = 4:1

In a proportion, the cross products are equal. To find the cross products, cross multiply. Multiply the numerator of one side to the denominator of the other side, and vice versa.

20/5 = 4/1

20(1) = 5(4)

20 = 20

If you are given three terms in a proportion, we can cross multiply to find the missing term. We use a variable (letter) to represent the missing term.

x/8 = 4/16

16x = 8(4)

16x = 32

x = 2

Students will then use these examples to solve the problems from Number Power 3: The Real World of Adult Math pages 72 - 75.