Writing and Solving Proportions

Writing and Solving Proportions

Chapter 6 Lesson 6.3

Writing and Solving Proportions

A proportion is an equation that states that two ratios are equivalent.

Equivalent Ratios

If one of the numbers in a proportion is unknown, you can solve the proportion to find the unknown number. One way to solve a proportion is to use mental math to find an equivalent ratio.

Problem Solving

• Each day, an elephant eats 5 pounds of food for every 100 pounds of its body weight. How much does a 9300 pound elephant eat per day?

• In Example 3, you’ll see how to use a proportion to answer this question.

Example 1 Solving a Proportion Using Equivalent Ratios

Solve the proportion

 $\frac{5}{6}=\frac{x}{18}$  

1. Compare the denominator
2. Find the x
Answer Because  $5\cdot3=15,\ x=15$  

Multiple Choice

Checkpoint 1:
Use equivalent ratios to solve the proportion.

 $\frac{2}{7}=\frac{x}{21}$  

• x= 8

• x= 4

• x= 9

• x= 13

Multiple Choice

Checkpoint 2:
Use algebra to solve the proportion.

 $\frac{5}{6}=\frac{x}{30}$   

• x=25

• x= 4.44

• x= 6.55