Carson Elementary And Intermediate Algebra 3e Page 3
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Carson Elementary and Intermediate Algebra 3e
Section 3.2
Solve percent problems using proportions.
To solve a percent problem, we can use one of the following proportions:
is
percent
percent
part
or
of
100
100
whole
Example 1:
What number is 15% of 36?
To use the proportion, identify the key words:
What number is 15% of 36?
We will use the first proportion. Fill in the 3 parts of the
proportion that you identified:
15 percent
x
15
What number is
36
100
Stays 100
of 36
Now, we use what we know about proportions to solve for
the missing number. By cross multiplying, we get the
following:
100
x
15
36
100
x
540
100
x
540
100
100
x
5
4 .
Therefore, 5.4 is 15% of 36.
Example 2:
48 is 120% of what number?
Identify the key words:
48 is 120% of what number?
We will use the first proportion. Fill in the 3 parts of the
proportion that you identified:
48
120
120 percent
48 is
x
100
of what number
Stays 100
Again, we use what we know about proportions to solve
for the missing number. By cross multiplying, we get the
following:
120
x
48
100
120
x
4800
120
x
4800
120
100
x
40
Therefore, 48 is 120% of 40.
C.Stewart 2011
page 3
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