Study Guide and Intervention - Houston ISD

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Study Guide and Intervention

Solving Proportions

A proportion is an equation stating that two ratios are equivalent. Since rates are types of ratios, they can also form proportions. In a proportion, a cross product is the product of the numerator of one ratio and the denominator of the other ratio.

Example 1 Determine whether 23 and 1105 form a proportion.

23 ? 1105 2 15 ? 3 10

Write a proportion. Find the cross products.

30 30

Multiply.

The cross products are equal, so the ratios form a proportion.

Example 2 Solve a8 1105 .

a8 1105

Write the proportion.

8 15 a 10

Find the cross products.

120 10a 11200 1100a

12 a

Multiply. Divide each side by 10. Simplify.

The solution is 12.

Exercises

Determine if the quantities in each pair of ratios are proportional. Explain.

1. 180 45

2. 94 161

3. 164 291

4. 1152 96

5. $42.o 4z8 $63.o 7z2

6. 152.75 gmali 152.60 gmali

Solve each proportion. 7. 7y 1268 9. 2b0 7208

8. 155 1w5 10. 582 m9

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Chapter 7

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