Pre-Algebra Chapter 6 - Ramsey School District

Study Tip
Base
In percent problems, the
base usually follows the
word of.
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• Updated data
• More activities
on finding a
percent.
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usa_today
Example 2
Find the Percent
What percent of 4 is 7?
Seven is being compared to 4. So, 7 is the part and 4 is the base.
Let p represent the percent.
a p
1 b 00 → 7 4 p
100 Replace a with 7 and b with 4.
7 · 100 4 · p Find the cross products.
700 4p Simplify.
70 0
4 p
4 4
Divide each side by 4.
175 p So, 175% of 4 is 7.
Example 3
Apply the Percent Proportion
ENVIRONMENT The
graphic shows the number
of threatened species in the
United States. What percent
of the total number of
threatened species are
mammals?
Compare the number of
species of mammals, 37, to the
total number of threatened
species, 443. Let a represent
the part, 37, and let b represent
the base, 443, in the percent
proportion. Let p represent
the percent.
a p
1 b 00 → 37
p
443
1 00
37 · 100 443 · p
3700 443p Simplify.
3 70
44
0
3
4 43p
4 Divide each side by 443.
43
8.4 p Simplify.
USA TODAY Snapshots ®
Number of threatened species in USA
Plants
168
Reptiles
27
Source: The International Union
for Conservation of Nature and
Natural Resources
Amphibians
25
Fish
131
Birds
55
By Hilary Wasson and Alejandro Gonzalez, USA TODAY
So, about 8.4% of the total number of threatened species are mammals.
Mammals
37
You can also use the percent proportion to find a missing part or base.
Types of Percent Problems
Type Example Proportion
Find the Percent 3 is what percent of 4? 3 4 p
100
Find the Part What number is 75% of 4? a 4 75
100
3 75
Find the Base 3 is 75% of what number? 1 b 00
www.pre-alg.com/extra_examples
Lesson 6-5 Using the Percent Proportion 289