Transcript Finding a Percent of a Number(6-4b).

COURSE 2 LESSON 6-4
Finding a Percent of a Number
Find each answer using mental math.
a. 49% of 300
What you think
49% is 50% – 1%
50% of 300 is 0.5 • 300, or 150.
1% of 300 is 0.01 • 300, or 3.
So 150 – 3 = 147.
Why it works
0.49 • 300
(0.50 – 0.01) • 300
(0.50 • 300) – (0.01 • 300)
150 – 3
147
Write 49% as a decimal.
Substitute 0.50 – 0.01 for 0.49.
Use the Distributive Property.
Multiply.
Simplify.
6-4
COURSE 2 LESSON 6-4
Finding a Percent of a Number
(continued)
b. 11% of 7220
What you think
11% is 10% + 1%
10% of 720 is 0.1 • 720, or 72.
1% of 720 is 0.01 • 720, or 7.2.
So 72 + 7.2 = 79.2.
Why it works
0.11 • 720
(0.10 + 0.01) • 720
(0.10 • 720) + (0.01 • 720)
72 + 7.2
79.2
Write 11% as a decimal.
Substitute 0.10 + 0.01 for 0.11.
Use the Distributive Property.
Multiply.
Simplify.
6-4
COURSE 2 LESSON 6-4
Finding a Percent of a Number
Estimate each answer.
a. 76% of 405
76% • 405
3
4
• 400 = 300
Write an expression.
Use compatible numbers such as 3 and 400.
4
Check for Reasonableness 76% of 405 is 0.76 • 405, or 307.8,
which is close to the estimate 300. The answer is reasonable.
b. 12% of 5,575
12% • 5,575
1
10 • 6,000 = 600
Write an expression.
Use compatible numbers such as 1 and 6,000.
10
Check for Reasonableness 12% of 5,575 is 0.12 • 5,575, or 669,
which is close to the estimate 600. The answer is reasonable.
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COURSE 2 LESSON 6-4
Finding a Percent of a Number
(continued)
c. 48% of 925
48% • 925
1
2
• 900 = 450
Write an expression.
Use compatible numbers such as 1 and 900.
2
Check for Reasonableness 48% of 925 is 0.48 • 925, or 444,
which is close to the estimate 450. The answer is reasonable.
6-4
COURSE 2 LESSON 6-4
Finding a Percent of a Number
Find the percent of each number.
1. 40% of 90
2. 120% of 45
36
3. 3.5% of 700
54
4. 90% of 650
24.5
585
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