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# How could we find the amount of wood needed to frame a poster made from a photo? PowerPoint PPT Presentation

How could we find the amount of wood needed to frame a poster made from a photo?. In this lesson you will learn how to compute an actual perimeter from a scale drawing by using ratios and proportions. A proportion is an equation that relates two equal ratios. For example:. =.

How could we find the amount of wood needed to frame a poster made from a photo?

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How could we find the amount of wood needed to frame a poster made from a photo?

In this lesson you will learn how to compute an actual perimeter from a scale drawing by using ratios and proportions.

A proportion is an equation that relates two equal ratios.

For example:

=

Find the length of TQ by cross multiplying

10

W

X

Q

6

R

15

?

(6)(15)

= (10)(TQ)

90

= (10)(TQ)

T

S

Z

Y

TQ = 9

Mixing up the order of one ratio in a proportion

8

11

=

16

B

22

M

-

12

L

24

N

A

C

Ratio of perimeters

4

A

B

8

Q

R

P = 8 + 6 + 8 + 6

3

P = (2 x 8) + (2 x 6)

C

D

6

P = 4 + 3 + 4 + 3

Perimeter = 28

P = (2 x 4) + (2 x 3)

T

S

Perimeter = 14

Perimeter of LMN = ?

MN :BC

= 18 : 24= 3 : 4

= 3 : 4

M

perimeter :PERIMETER

18

L

= 16 + 24 + 30 = 70

PERIMETER

N

B

=

16

210

= 4(perimeter)

24

A

perimeter = 52.5

30

C

How large is the frame?

= 2 : 15

= 4 : 30

small : LARGE

4 in

= 2(6) + 2(4) = 20 in

perimeter

6 in

=

= 300

2P

30 in

P = 150 in

In this lesson you have learnedhow to compute an actual perimeter from a scale drawing by using ratios and proportions.

Find the base of the large triangle if the scale factor of the small perimeter to the large perimeter is 3 : 5 for these similar triangles.

6

6

15

If the scale factor of a small figure to a large figure is 3 to 7, what will be the scale factor of the large figure’s perimeter to the small figure’s perimeter? Explain.

• Find the length of side DF.

7 cm

15 cm

E

Q

? cm

P

Perimeter of PQR = 40 cm

R

D

Perimeter of DEF = 90 cm

F

1. Find the perimeter of the large rectangle.

84

16

28

2. If the scale factor of the large perimeter

to the small perimeter is 9:5, find the

B

17

C

M

L

16

12

K

N

30

A

D