# Using Proportional Reasoning

## Lesson Preview

## What You'll Learn- To use unit rates to solve proportions
- To solve proportions involving variables
## … And WhyTo calculate a cost, as in Example 1 |

## Solving Proportions Using Unit Rates

##### Reading Math

Sometimes mi/gal is written as mpg.

Suppose you know that your car gets 29 mi/gal and you have 10 gal of gas. You estimate that you can go 29 • 10, or 290, miles before you run out of gas. You are using a unit rate and multiplying.

You can use unit rates to solve a proportion. First find the unit rate. Then multiply to solve the problem.

#### Using Unit Rates

ShoppingUse the information at the right to find the cost in dollars of 8 oranges.

Solve the proportion =

- Find the unit price.

- You know the cost of one orange. Multiply to find the cost of 8 oranges.

The cost of 8 oranges is $3.12.