Unit 7: Similarity(7.1) Ratios and Proportions

LT: Write and solve proportions

Ratios

Ratio: A comparison of two quantities by division.

1) The ratio of a to b

2) a : b

3) a

b, b0

Ratios can be written in three ways…

5 in.

Ratios

6 in.

1 ¾ ft.

2 ft.

Find the ratio of the width of the photo to the poster.

Proportions

Proportion: A statement that two ratios are equal.

a

bc

dor a :bc : d

Determine if each of the following pairs of ratios are equal.

1) 1: 2 5 :105

3

3

5 2)

3) 10

15

18

27= ≠ =

Proportions

Properties of Proportions: is equivalent to…

a

bc

d

1) ad bc

2) b

ad

c

3) a

cb

d

4) a bb

c dd

Cross-Product Property: The product of the extremes is equal to the product of the means.

If , complete each statement.

Applying Properties

x

y

5

6

1) 6x

2) y

x

3) x

5

4) x yy

Solving Proportions

Solve the following proportions.

1) x

6

12

8

2) y 3

8y

4

3) 5

z

20

3

Ratios

Scale: The ratio of any length in a scale drawing to the corresponding actual length.

Ex. 1cm to 1ft or 1in = 10ft or 1mm : 100mi

An inch ruler shows that l = 7/8 in.Find the actual length of the bedroom.

7.1 Ratios and Proportions

HW (7.1): Pgs. 368-370; 1-29 odd, 43, 44