 # Explain Ratio 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

• 10 to 15
• 10:15

• 10
---
15

## More Ratio Resources

* AAA Math
* Algebra Help
* BBC Skillwise
* Get Help with Ratios
* Math.com
* Purple Math

We can use an equation to show that two ratios are equivalents of each other. The proportion can be expressed in two ways:

• 10:15 = 2:3

• 10   =    2
---         ---
15         3

If you want to figure out a ratio that's the equivalent of another ratio, cross multiplying can be used to find the unknown number. For example, cross-multiply (multiply in each direction diagonally) to find the missing number (x) in the proportion below:

8     =     x
---          ---
10         50

10 times x is 10x, and 8 times 50 is 400, so we can write this as

10x = 400   (this means "10 times what equals 400?")

Since 10 x 40 = 400,

8     =     40
---           ---
10          50

Ratio Lesson Plans

Ratio Worksheets

Ratio Interactive Activities

Updated 10/13/2013