Transcript Proportions_Examples.ppt

Ratios and Proportions
Lesson 7-1
Additional Examples
A scale model of a car is 4 in. long. The actual car
is 15 ft long. What is the ratio of the length of the model to
the length of the car?
Write both measurements in the same units.
15 ft = 15 X 12 in. = 180 in.
length of model
4 in.
4 in.
4
1
= 15 ft. =
=
=
180 in. 180 45
length of car
The ratio of the length of the scale model to the length of the car
is 1 : 45.
Geometry
Ratios and Proportions
Lesson 7-1
Geometry
Additional Examples
Complete: If a = 12 , then b = ? .
4
b
12
a
12
 4b =
 4b
4
b
Multiply each side by 4b.
ab = 48
Cross-Product Property
ab
48
=
12a
12a
Divide each side by 12a.
b
4
=
12
a
Simplify.
?
Ratios and Proportions
Lesson 7-1
Geometry
Additional Examples
Solve each proportion.
2
n
x+1 x
=
3
2
a. 5 = 35
b.
5n = 2(35) Cross-Product Property
3x = 2(x + 1) Cross-Product Property
5n = 70
3x = 2x + 2
n = 14
Simplify.
Divide each side by 5.
x=2
Use the Distributive Property.
Subtract 2x from each side.
Ratios and Proportions
Lesson 7-1
Geometry
Additional Examples
1
2
Two cities are 3 in. apart on a map with the scale
1 in. = 50 mi. Find the actual distance.
Let d represent the actual distance.
Map distance (in.) = 1 in.
actual distance (mi.) 50 mi.
1
32
1
Substitute.
d = 50
d = 50(3 1 )
Use the Cross-Product Property.
d = 175
Simplify.
2
The cities are actually 175 mi. apart.