Download Using Proportions Math Skills LESSON 3

Name
Date
Class
Math Skills
LESSON 3
Using Proportions
A proportion is an equation that shows that two ratios are equal. When two ratios form a
proportion, the cross products are equal. In this example, the cross products are 2 × 10 and
4 × 5.
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If 2 × 10 = 4 × 5, then 4__2 = ___
.
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If one of the numbers in a proportion is unknown, cross multiply to change the proportion
to an equation. Then solve the equation for the unknown number.
About 30 hair follicles can be found in 1 cm2 of a sample of skin. How many hair follicles
are in 6 cm2 of that skin?
Step 1 Use the information in the problem to write a proportion.
30
___
= 6__n
1
Step 2 Cross multiply to solve for the unknown number.
1 × n = 30 × 6
n = 180
Step 3 Use the solution to answer the question in the original problem situation.
There are 180 hair follicles in 6 cm2 of the sample of skin.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Practice
1. About 30 hair follicles can be found in
3. If 450 sweat glands are found in 1 cm2
1 cm2 of skin. How many hair follicles
are in 12 cm2 of that skin?
of skin, how many sweat glands are in
16 cm2 of that skin?
2. If you found 7 blades of grass in 1 cm2
4. If 750 sweat glands are found in 2 cm2
of lawn, how many blades of grass
would you find in 8 cm2 of lawn?
Structure and Movement
of skin, how many sweat glands are in
9 cm2 of that skin?
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