# What is a scale factor and how do you compute one? - PowerPoint PPT Presentation

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What is a scale factor and how do you compute one?. Happy Town. Smile City. Funville. Scale in miles: 1 inch = Approx. 15 miles. Gladberg. In this lesson you will learn how to determine the scale factor between two similar figures by applying ratios.

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What is a scale factor and how do you compute one?

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What is a scale factor and how do you compute one?

Happy Town

Smile City

Funville

Scale in miles:

1 inch = Approx. 15 miles

In this lesson you will learn how to determine the scale factor between two similar figures by applying ratios.

A ratio is a comparison between two numbers.

For example:

# Apples : # Oranges

or 2 : 1

= 4 : 2

Reversing the order of the ratio

For example:

# Apples : # Oranges

-

= 2 : 4 or 1 : 2

Two figures are similar if the lengths of every pair of corresponding sides are in the same ratio.

=

=

8

B

M

11

=

=

16

22

12

L

=

=

N

A

24

C

The scale factor is the ratio of the lengths of corresponding sides in similar figures.

6

W

X

Q

4

R

4

T

S

=

=

=

=

Z

Y

6

Scale factor of large to small

Scale factor of small to large

Scale factor on a map:

The number of inches on the map that corresponds to the actual number of miles

3 inches

45 miles

Smile City

Happy Town

Funville

Scale in miles:

1 inch = Approx. 15 miles

In this lesson you have learned how to determine the scale factor between two similar figures by applying ratios.

Find the scale factor of the small triangle to the large triangle.

40

10

10

25

25

16

Describe in words what it means when a diagram is drawn in a 1:10 scale.

• Find the scale factor of triangle DEF to triangle PQR.

9

15

E

Q

P

42

Perimeter of PQR = 42

R

D

F

1. Find the scale factor of the small rectangle to the large rectangle.

32

80

12

30

2. Find the scale factor of the large triangle to the small triangle.

26

14

B

M

L

20

45

A

N

C