USING PROPORTIONS(OBJECTIVE: USING PROPORTIONS TO SOLVE REAL WORLD PROBLEMS)

MS. BATTAGLIA/ MR. BALDINO

WORK TOGETHER

A ratio is a comparison of two numbers by division. For example, ½ and 5:2 are ratios. The scale of a blueprint is the ratio of a length on the blueprint to the actual length it represents. Turn to page 158 in your textbooks and work on “Work Together” with a partner.

USING PROPERTIES OF EQUALITY

A proportion is a statement that two ratios are equal. Another way to write the sample at the right is 3:4 = 12:16. Read this “3 is to 4 as 12 is to 6.”

To solve a proportion with a variable, you can use the multiplication property of equality.

EXAMPLE

Solve

USING CROSS PRODUCTS

The numerators and denominators of the ratios that form a proportion have a special relationship. The cross products of a proportion are equal.

When b ≠ 0 and d ≠ 0,

If then

EXAMPLE

EXAMPLE

ΔABC is similar to ΔDFE. AB = 15, BC = 18, AC = 21, DF = 10.

Find DE.

Similar figures have the same shape, but not necessarily the

same size.

AQUACULTURE

In 1994, U.S. trout farms produced 52,000,000 lb of trout. Suppose a trout farmer raised 858,000 lb of trout. What percent of the 1994 U.S. trout production did the farmer raise? Round our answer to the nearest tenth of a percent.

CLASSWORK/ HOMEWORK

4-1 Worksheet