Definitions:

A ratio is an ordered pair of numbers a and b, written a / b where b does not equal 0.

A proportion is an equation in which two ratios are set equal to each other.

For example, if there is 1 boy and 3 girls you could write the ratio as:

• 1 : 3 (for every one boy there are 3 girls)
• 1 / 4 are boys and 3 / 4 are girls
• 0.25 are boys (by dividing 1 by 4)
• 25% are boys (0.25 as a percentage)

Introduction to Ratios

Watch a Khan Academy Video » Length: 14:13

Understanding Proportions

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Length: 10:25

Simplifying Rates and Ratios

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Length: 2:28

Find an Unknown in a Proportion

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Length: 5:48