ExplainRatio and Proportion
A ratio is a comparison of two numbers. For example, if 25 students -- 10 boys and 15 girls -- are in your class, then the ratio of boys to girls is 10 to 15. A ratio can be expressed in three ways. The ratio of boys to girls in your class might be expressed as
A proportion is a statement (or equation) that says two ratios are equal. A proportion can be expressed in two ways:
An important fact to know about proportions, is that if one of the numbers in a proportion is not known, cross multiplying can be used to find the unknown number. For example, cross multiply to find the missing number in the proportion below:
? 2 2 x 15 = 30 -- = -- 15 3 3 x ? = 30 The missing number, therefore, is 10.
Ratio Lesson Plans
Ratio Interactive Activities