CatalystThursday, October 6, 2011

Of the 75 teachers at a school, 15 teach mathematics. What percent of the teachers at the school teach mathematics?

A. 2% B. 5%C. 15% D. 20%

RATIOS and PROPORTIONS REVIEW

By: Teachers who care!

RATIOS & PROPORTIONS A ratio is a comparison of two

numbers by division. To write ratios, use the word to, a

colon, or a fraction bar.EXAMPLE #1: John read 3 books in 4

days. Write the ratio of books to days.

Words: 3 to 4

Colon: 3:4

Fraction: 3/4

RATIOS & PROPORTIONS A proportion is a statement that

two ratios are equal.

EXAMPLE#2: Is a proportion?15

6

5

2

Find the cross products.

65152 30 = 30 TRUEIf TRUE, the

statement is a proportion.

RATIOS & PROPORTIONS

EXAMPLE#3: Is a proportion?

5

3

7

4

Find the cross products.

3754 20 = 21 FALSEIf FALSE, the

statement is NOT a proportion.

RATIOS & PROPORTIONS

EXAMPLE#4: Solve the proportion:10

4

5

Find the cross products.

4510 x2010 x

10 10

2x

Divide both sides by 10.

RATIOS & PROPORTIONS

There are 5 boys and 6 girls in Grant School.

1. What is the ratio of girls to boys using a fraction? 5

6

2. What is the ratio of girls to children in Grant School (use a colon)? 6:11

3. What is the ratio of boys to children in Grant School (use words)?

5 to 11

RATIOS & PROPORTIONS

Are the following proportions?

7

3

9

4

20

9

9

4

27

12

9

4

18

8

9

4

3974 2728

FALSE – Not a proportion

99204 8180

FALSE – Not a proportion

129274 108108

TRUE – this is a proportion

89184 7272

TRUE – this is a proportion

RATIOS & PROPORTIONS

Find the missing numbers to make the following proportions.

21

93

9213 x

x963

x79 9

10

5

4

5410 x2010 x

10 10 2x

9

12

3

4

1

941 x36x

SCALE DRAWINGS A scale drawing is a drawing of an

object with dimensions proportional to those of the actual object. To find lengths from scale drawings, set up and solve proportions.

SCALE DRAWINGS USING PROPORTIONSEXAMPLE#1: ¼ in = 5 ft is a scale

for a rock band’s concert stage.

A. The scale length of the drum stand is 1 in. What is the actual length of the drum stand?

)(

)(

)(

)(

actualobject

drawingobject

ftactual

indrawing

x

1

5

25.

Cross multiply.

1525. x525. x

.25 .2520x

Divide by .25

SCALE DRAWINGS USING PROPORTIONSEXAMPLE#2: ¼ in = 5 ft is a scale

for a rock band’s concert stage.

B. The actual length of the stage is 60 ft. What is the scale length of the stage?

)(

)(

)(

)(

actualobject

drawingobject

ftactual

indrawing

605

25. x

Cross multiply.

x 56025.x515

5 5x3

Divide by 5

SCALE DRAWINGS USING PROPORTIONSGiven a scale of ½ in = 4 ft, find the actual

length for each scale length given.

x

75.2

4

5.

75.245. x115. x

.5 .5

ftx 22

in4

32 in5

x

5

4

5.

545. x205. x

.5 .5

ftx 40

Your Turn to Show What You Know

Yes, you will use the calculator; to show your work, you will set the problem up to show me you know what to do

Pages 142-143, 194-195, and 264-265* Only answer the multiple choice

questions!!!