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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:. =.
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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.
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
length of AD.
B
17
C
M
L
16
12
K
N
30
A
D