Finding Percents

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Finding Percents
Warm Up
Problem of the Day
Lesson Presentation
Pre-Algebra
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• Warm Up
• Rewrite each value as indicated.
• 1. as a percent
• 2. 25 as a fraction
• 3. as a decimal
• 4. 0.16 as a fraction

48
0.375
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Problem of the Day A number between 1 and 10 is
halved, and the result is squared. This gives an
answer that is double the original number. What
is the starting number?
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Learn to find percents.
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Relative humidity is a measure of the amount of
water vapor in the air. When the relative
humidity is 100, the air has the maximum amount
of water vapor. At this point, any additional
water vapor would cause precipitation. To find
the relative humidity on a given day, you would
need to find a percent.
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Additional Example 1A Finding the Percent One
Number Is of Another
A. What percent of 220 is 88?
Method 1 Set up an equation to find the percent.
p ? 220 88 Set up an equation.
p 0.4 0.4 is 40.
So 88 is 40 of 220.
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Additional Example 1B Finding the Percent One
Number Is of Another
B. Eddie weighs 160 lb, and his bones weigh 24
lb. Find the percent of his weight that his
bones are.
Method 2 Set up a proportion to find the percent.
Think What number is to 100 as 24 is to 160?
Set up a proportion.
Substitute.
n ? 160 100 ? 24
Find the cross products.
160n 2400
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Additional Example 1 Continued
Solve for n.
n 15
The proportion is reasonable.
So 15 of Eddies weight is bone.
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Try This Example 1A
A. What percent of 110 is 11?
Method 1 Set up an equation to find the percent.
p ? 110 11 Set up an equation.
p 0.1 0.1 is 10.
So 11 is 10 of 110.
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Try This Example 1B
B. Jamie weighs 140 lb, and his bones weigh 21
lb. Find the percent of his weight that his
bones are.
Method 2 Set up a proportion to find the percent.
Think What number is to 100 as 21 is to 140?
Set up a proportion.
Substitute.
n ? 140 100 ? 21
Find the cross products.
140n 2100
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Solve for n.
n 15
The proportion is reasonable.
So 15 of Jamies weight is bone.
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Additional Example 2A Finding a Percent of a
Number
Choose a method Set up an equation.
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Additional Example 2A Continued
The reservoir contained 38,000,000 gallons of
water after the drought.
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Additional Example 2B Finding Percents
B. Ms. Chang deposited 550 in the bank. Four
years later her account held 110 of the original
amount. How much money did Ms. Chang have in the
bank at the end of the four years?
Choose a method Set up a proportion.
110 ? 550 100 ? a Find the cross products.
60,500 100a
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Additional Example 2B Continued
605 a Solve for a.
Ms. Chang had 605 in the bank at the end of the
four years.
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Try This Example 2A
Choose a method Set up an equation.
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Try This Example 2A
w 30,400,000
The water flow in the river was 30,400,000
gallons per day after the drought.
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Try This Example 2B
B. Mr. Downing deposited 770 in the bank. Four
years later his account held 120 of the original
amount. How much money did Mr. Downing have in
the bank at the end of the four years?
Choose a method Set up a proportion.
120 ? 770 100 ? a Find the cross products.
92,400 100a
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Try This Example 2B Continued
924 a Solve for a.
Mr. Downing had 924 in the bank at the end of
the four years.
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Lesson Quiz
Find each percent to the nearest tenth. 1. What
percent of 33 is 22? 2. What percent of 300 is
120? 3. 18 is what percent of 25? 4. The volume
of Lake Superior is 2900 mi3 and the volume of
Lake Erie is 116 mi3. What percent of the volume
of Lake Superior is the volume of Lake Erie?
66.7
40
72
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