7.2 writing and solving proportions 1

Lesson 7.1, For use with pages 343-346

Write two fractions that are equivalent to the given fraction.

1.129 2. 26

30

Lesson 7.1, For use with pages 343-346

Write two fractions that are equivalent to the given fraction.

1.129 2. 26

30

ANSWER 34’1216

ANSWER 1315’

3945

7.2 Writing and Solving 7.2 Writing and Solving ProportionsProportions

Essential Questions Questions

What is the connection between a ratio and a fraction?

Why are ratios and proportions important?

How are scale drawings, models, and proportions used in everyday life?

A proportion is an equation stating that two ratios are equal.

For example:

If cross products are equal, the ratios form a proportion.

3 6

8 16

A 5 lb. free weight costs $2.35. A 12 lb. free weight cost $5.64. Are these prices proportional to their weights?

2.35 ? 5.64

5 = 12

Note: cross products are equal – Yes, prices are proportional to their weight.

EXAMPLE 1 Writing and Solving a Proportion

An adult rhinoceros beetle weighs only 0.525 ounce but can carry about 446.25 ounces on its back. If a person were proportionately as strong as a rhinoceros beetle, how much weight could a 100 pound person carry?

SOLUTION

Use a table to set up a proportion.

446.250.525 = x

100 Write a proportionouncesounces = pounds

pounds.

446.250.525 100 =

x100 100 Multiply each side by 100.

Simplify.

EXAMPLE 1 Writing and Solving a Proportion

85,000 x=

If human strength were proportional to that of a rhinoceros beetle, a 100 pound person could carry 85,000 pounds.

ANSWER

Leigh’s copy machine can make 15 copies in 1 minute. She has a script with 75 pages. How many minutes will it take to copy the script?

Use a proportion with labels and a variable:

copies

minutes

Larry mixes concrete for a construction firm. To make 3 cubic feet of concrete, Larry uses 70 pounds of cement. How many pounds of cement would Larry use to make one cubic foot?

The sign advertises “2 pounds of potatoes for 88 cents.” How much should 5 pounds cost?

A recipe for 30 cookies uses 2 cups of flour. If you need to make 75 cookies, how much flour will be needed?

Homework

Worksheet 7.2