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8.84 divided by 3.4 is 2.6. Practice Problem Divide 75.6 by 3.6.

Use Proportions

An equation that shows that two ratios are equivalent is a proportion. The ratios —

and — are equivalent, so they can be written as 4 = 454. This equation is a proportion.

When two ratios form a proportion, the cross products are equal. To find the cross products in the proportion 4 = 454, multiply the 2 and the 10, and the 4 and the 5. Therefore 2 X 10 = 4 X 5, or 20 = 20.

Because you know that both proportions are equal, you can use cross products to find a missing term in a proportion. This is known as solving the proportion.

Example The heights of a tree and a pole are proportional to the lengths of their shadows.The tree casts a shadow of 24 m when a 6-m pole casts a shadow of 4 m.What is the height of the tree?

Step 1 Write a proportion.

height of tree = length of tree's shadow height of pole length ofpole's shadow

Step 2 Substitute the known values into the proportion. Let h represent the unknown value, the height of the tree. h = 24 6 4

Step 4 Simplify the equation. 4h = 144

The height of the tree is 36 m.

Practice Problem The ratios of the weights of two objects on the Moon and on Earth are in proportion. A rock weighing 3 N on the Moon weighs 18 N on Earth. How much would a rock that weighs 5 N on the Moon weigh on Earth?

### Use Percentages

The word percent means "out of one hundred." It is a ratio that compares a number to 100. Suppose you read that 77 percent of the Earth's surface is covered by water. That is the same as reading that the fraction of the

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