Transcript 1 - Jefferson School District

6-3 Estimating with Percents
California
Standards
NS1.4 Calculate given percentages
of quantities and solve problems involving
discounts at sales, interest earned, and tips.
Also covered: NS2.1
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6-3 Estimating with Percents
The table shows common percents and their
fraction equivalents. You can estimate a percent of
a number by substituting a fraction that is close to
a given percent.
Percent
10%
20%
Fraction
1
10
1
5
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25%
1
33 3%
50%
2
66 3%
1
4
1
3
1
2
2
3
6-3 Estimating with Percents
Additional Example 1: Using Fractions to Estimate
Percents
Use a fraction to estimate 27% of 63.
Think: 27% is about 25% and
1
25% is equivalent to .
4
 1  60 Change 63 to a compatible
4
number.
 15
Multiply.
27% of 63 is about 15.
27% of 63  1  63
4
Remember!
Compatible numbers are close to the numbers in the problem
and help you use mental math to find a solution.
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6-3 Estimating with Percents
Check It Out! Example 1
Use a fraction to estimate 48% of 91.
48% of 91  1  91
2
Think: 48% is about 50% and
1
50% is equivalent to .
2
 1  90
2
Change 91 to a compatible
number.
 45
Multiply.
48% of 91 is about 45.
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6-3 Estimating with Percents
Additional Example 2: Consumer Math Application
Tara’s T’s is offering 2 T-shirts for $16, while
Good-T’s is running their buy one for $9.99, get one
for 50% off sale. Which store offers the better deal?
First find the discount price for 2 t-shirts at Good T’s.
50% of $9.99 =
1
1
2  $9.99 Think: 50% is equivalent to 2 .
1  $10

2
Change $9.99 to a
compatible number.
 $5
Multiply.
The second shirt cost approximately $5. Since $10 + $5
= $15, the 2 T-shirts for $15 at Good-T’s is the better
deal.
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6-3 Estimating with Percents
Check It Out! Example 2
Billy’s Office Supply Store is offering 25% off a
leather notebook, originally priced at $9.75. K’s
Office Supply Store offers the same notebook, not
on sale, at $7.00. Which store offers the better deal?
First find the discount on the notebook at Billy’s Office Supply.
1
1  $9.75
Think: 25% is equivalent to 4 .
25% of $9.75 =
4

1  $10
4
 $2.50
Change $9.75 to a compatible
number.
Multiply.
The discount is approximately $2.50. Since $10 – $2.50 = $7.50,
the notebook from K’s Office Supply Store is the better deal.
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6-3 Estimating with Percents
Another way to estimate percents is to find
1% or 10% of a number. You can do this
by moving the decimal point in the number.
1% of 45 = 0. 45. 10% of 45 = 45
. .
To find 1% of a
number, move the
decimal point two
places to the left.
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To find 10% of a
number, move the
decimal point one
place to the left.
6-3 Estimating with Percents
Additional Example 3: Estimating with Simple
Percents
Use 1% or 10% to estimate the percent of
each number.
A. 4% of 18
18 is about 20, so find 4% of 20.
1% of 20 =.20.
4% of 20 = 4  0.2 = 0.8 4% equals 4 · 1%.
4% of 18 is about 0.8.
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6-3 Estimating with Percents
Additional Example 3: Estimating with Simple
Percents
Use 1% or 10% to estimate the percent of
each number.
B. 29% of 80
29% is about 30, so find 30% of 80.
10% of 80 = 80.
.
30% of 80 = 3

8.0 = 24.0 30% equals 3 · 10%.
29% of 80 is about 24.
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6-3 Estimating with Percents
Check It Out! Example 3
Use 1% or 10% to estimate the percent of
each number.
A. 5% of 14
14 is about 15, so find 5% of 15.
1% of 15 =. 15.
5% of 15 = 5

0.15 = 0.75
5% of 14 is about 0.75.
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5% equals 5 · 1%.
6-3 Estimating with Percents
Check It Out! Example 3
Use 1% or 10% to estimate the percent of
each number.
B. 21% of 60
21% is about 20, so find 20% of 60.
10% of 60 = 60.
.
20% of 60 = 2

6.0 = 12.0 20% equals 2 · 10%.
21% of 60 is about 12.
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6-3 Estimating with Percents
Additional Example 4: Consumer Math Application
Tim spent $58 on dinner for his family. About how
much money should he leave for a 15% tip?
Since $58 is about $60, find 15% of $60.
15% = 10% + 5%
10% of $60 = $6
5% of $60 = $6 ÷ 2 = $3
$6 + $3 = $9
Think: 15% is 10% + 5%.
1
5% is 2 of 10% so divide
$6 by 2.
Add the 10% and 5%
estimates.
Tim should leave about $9 for a 15% tip.
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6-3 Estimating with Percents
Check It Out! Example 4
Amanda spent $12 on a hair cut. About how
much money should she leave for a 15% tip?
Since $12 is about $10, find 15% of $10.
15% = 10% + 5%
Think: 15% is 10% + 5%.
10% of $10 = $1
1
5% of $10 = $1 ÷ 2 = $0.50 5% is 2 of 10% so divide
$1 by 2.
Add the 10% and 5%
$1 + $0.50 = $1.50
estimates.
Amanda should leave about $1.50 for a 15% tip.
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