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Section 3.8
Ratios & Rates
Made
Easy
Mr.
Beltz
&
Mr. Sparks
Ratio
A ratio is a comparison of a number “A” to another
number “B” using division.
Three ways to express a ratio
A to B
A:B
A
B
Ways to write Ratio’s
PART
1 = .25 or 25%
WHOLE
4
or
PART : WHOLE
1: 4
= 25%
Proportions
A proportion is an equation stating that two ratios are
equivalent. It can be written in two ways:
4:8 = 8:16
Or
4= 8
8 16
(8 * 8 =64)
(4 * 16 = 64)
Solving for Variables
4= 8
8 X
4x = 8 * 8
4x = 64
4x = 64
4
4
x = 16
Practice: Mental Math
2=6
5 X
8=4
x 3
3=X
4 20
Using Units
Important! Always keep the units lined up!
Example:
1 cm : 4 m
12 cm : X m
CM
M
1 cm = 12 cm
4m
Xm
Using Units
Important! Always keep the units lined up!
Example:
1 cm : 4 m
12 cm : X m
CM
M
1 cm = 12 cm
4m
Xm
x = 12 * 4
x=48