Find the Original Number
12-5
25% of Marlo’s savings is in a shoebox
under her bed. The shoebox has $45 in
it. How much has Marlo saved in all?
Let stotal savings.
25% of s$45
s$45
s $45
s$180
Marlo has saved $180 in all.
4
1
4
1
1
4
1
4
percentageratebase prb
original number (total number)
Write and solve a proportion.
45 b 900
45 b 45 900 45
b 20
part
whole
9
b
45
100
part
whole
0% 45% 100%
0 9 b
Of the people at the bowling alley,
45% play for the bowling league. There are
a total of 9 bowling league players. How
many people are at the bowling alley?
To find how many people, the original
number or base, write and solve an
equation or a proportion.
45% of what numberis 9?
Let bequal the total number of people.
Write and solve an equation.
45% of b 9
0.45b 9
0.45b0.45 9 0.45
b 20
45% of 20 is 9.
So there are 20 people at the bowling alley.
Study these examples.
Divide both
sides by 0.45.
If Mike’s savings of $268.80 is 42% of
his savings goal, what amount of money
does Mike want to save?
42% of s$268.80
0.42s$268.80
s$640
Mike wants to save $640.
$268.80
0.42
0.42s
0.42
Think
42% 0.42
1.4
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