8-10 Using Percents
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8-10 Using Percents
Find the percent of each number.
1. 75% of 300
2. 93% of 56
3. 32% of 128
4. 9% of 60
225
52.08
40.96
5.4
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8-10 Using Percents
A chessboard is 8 squares wide by 8 squares long. Each player has 8 pawns,
1 king, and 7 other pieces. At the start of a game, all the pieces are on the board, 1 piece per square. What percent of the total number of squares have a chess piece?
50%
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8-10 Using Percents
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8-10
Course 1

8-10 Using Percents
Common Uses of Percents
Discounts A discount is an amount that is subtracted from the regular price of an item.
discount = price • discount rate total cost = price – discount
Tips A tip is an amount added to a bill for service.
tip = bill • tip rate total cost = bill + tip
Sales tax Sales tax is an amount added to the price of an item.
sales tax = price • sales tax rate total cost = price + sales tax
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8-10 Using Percents
Additional Example 1: Finding Discounts
A clothing store is having a 10% off sale. If
Angela wants to buy a sweater whose regular price is $19.95, about how much will she pay for the sweater after the discount?
Step 1: First round $19.95 to $20.
Step 2: Find 10% of $20 by multiplying 0.10 • 20.
(Hint: Moving the decimal point one place left is a shortcut.)
10% of 20 = 0.10 • $20 = $2.00
The approximate discount is $2.00. Subtract this amount from $20.00 to estimate the cost of the sweater.
$20.00 – $2.00
= $18.00
Angela will pay about $18.00 for the sweater.
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8-10 Using Percents
Remember!
To multiply by 0.10, move the decimal point one place left.
Course 1

8-10 Using Percents
Try This: Example 1
A fishing store is having a 10% off sale. If
Gerald wants to buy a fishing pole whose regular price is $39.95, about how much will he pay for the pole after the discount?
Step 1: First round $39.95 to $40.
Step 2: Find 10% of $40 by multiplying 0.10 • 40.
10% of 40 = 0.10 • $40 = $4.00
The approximate discount is $4.00. Subtract this amount from $40.00 to estimate the cost of the pole.
$40.00 $4.00
= $36.00
Gerald will pay about $36.00 for the fishing pole.
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8-10 Using Percents
When estimating percents, use percents that you can calculate mentally.
• You can find 10% of a number by moving the decimal point one place to the left.
• You can find 1% of a number by moving the decimal point two places to the left.
• You can find 5% of a number by finding onehalf of 10% of the number.
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8-10 Using Percents
Additional Example 2: Finding Tips
Ben’s dinner bill is $7.85. He wants to leave a tip that is 15% of the bill. About how much should his tip be?
Step 1: First round $7.85 to $8.
Step 2: Think: 15% = 10% + 5%
10% of $8 = 0.10 • $8 = $0.80
Step 3: 5% = 10% ÷ 2
= $0.80 ÷ 2 = $0.40
Step 4: 15% = 10% + 5%.
= $0.80
+ $0.40 = $1.20
Ben should leave about $1.20 as a tip.
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8-10 Using Percents
Try This: Example 2
Lita’s dinner bill is $11.95. She wants to leave a tip that is 15% of the bill. About how much should her tip be?
Step 1: First round $11.95 to $12.
Step 2: Think: 15% = 10% + 5%
10% of $12 = 0.10 • $12 = $1.20
Step 3: 5% = 10% ÷ 2
= $1.20 ÷ 2 = $0.60
Step 4: 15% = 10% + 5%.
= $1.20
+ $0.60 = $1.80
Lita should leave about $1.80 as a tip.
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8-10 Using Percents
Additional Example 3: Finding Sales Tax
Ann is buying a dog bed for $29.75. The sales tax rate is 7%. About how much will the total cost of the dog bed be?
Step 1: First round $29.75 to $30.
Step 2: Think: 7% = 7 • 1%
1% of $30 = 0.01 • $30 = $0.30
Step 3: 7% = 7 • 1%.
= 7 • $0.30
= $2.10.
The approximate sales tax is $2.10. Add this amount to $30 to estimate the total cost of the dog bed.
$30 + $2.10 = $32.10
Ann will pay about $32.10 for the dog bed.
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8-10 Using Percents
Try This: Example 3
Erik is buying a blanket for $19.83. The sales tax rate is 8%. About how much will the total cost of the blanket be?
Step 1: First round $19.83 to $20.
Step 2: Think: 8% = 8 • 1%
1% of $20 = 0.01 • $20 = $0.20
Step 3: 8% = 8 • 1%
= 8 • $0.20
= $1.60.
The approximate sales tax is $1.60. Add this amount to $20 to estimate the total cost of the blanket.
$20 + $1.60 = $21.60
Erik will pay about $21.60 for the blanket.
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8-10
Lesson Quiz
1. Sean’s new jeans are priced at $29.97, but the sale sign reads, “Take 15% off.” About how much will the jeans cost after the discount? About $25.50
2. The bill for a family dinner comes to $56.78.
About how much would a 20% tip be?
About $11.50
3. The price on a book is $12.99. If sales tax is
4%, about how much will its total cost be?
About $13.50
4. Megan wants a new bike. She is happy to see a sign that reads, “All bikes 10% off.” If the original price of the bike was $159.90 and sales tax is 6%, about how much will the total cost of the bike be?
About $150
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