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Method 2: Use 10% to estimate.
10% of 100 is 10.
92% is about 9 • 10%.
9 • 10 = 90
So, 92% of 104 is about 90.
2-2 Percent and Estimation
Estimate.
21. 76% of 180
24. SOLUTION: Method 1: Use a fraction to estimate.
% of 412
SOLUTION: % is one-half of 1%. 412 is about 400.
76% is about 75% or
.
Method 2: Use 10% to estimate.
10% of 180 is 18.
76% is about 7.5 • 10%.
7.5 • 18 = 135
So, 76% of 180 is about 135.
22. 57% of 29
SOLUTION: Method 1: Use a fraction to estimate.
57% is about 60% or
. 29 is about 30.
One half of 4 is
So,
• 4 or 2.
% of 412 is about 2.
25. 0.9% of 74
SOLUTION: 0.9% is nine-tenths of 1%. 74 is about 70.
So, 0.9% of 74 is about 0.7.
26. 32% of 89.9
SOLUTION: Method 2: Use 10% to estimate.
10% of 30 is 3.
57% is about 6 • 10%.
6 • 3 = 18
So, 57% of 29 is about 18.
32% is about 33% or
32% of 89.9 ≈ . 89.9 is about 90.
or 30
So, 32% of 89.9 is about 30.
23. 92% of 104
SOLUTION: Method 1: Use a fraction to estimate.
92% is about 90% or
. 104 is about 100.
Method 2: Use 10% to estimate.
10% of 100 is 10.
92% is about 9 • 10%.
9 • 10 = 90
So, 92% of 104 is about 90.
24. % of 412
SOLUTION: % is one-half of 1%. 412 is about 400.
27. You use 43 muscles to frown. When you smile, you
use 32% of these same muscles. About how many
muscles do you use when you smile?
SOLUTION: Estimate 32% of 43.
Method 1: Use a fraction to estimate.
32% is about 30% or
32% of 43 ≈ . 43 is about 40.
• 40 or 12
Method 2: Use 10% to estimate.
10% of 40 is 4.
32% is about 3 • 10%.
3 • 4 = 12
So, 32% of 43 is about 12.
You use about 12 muscles when you smile.
28. Justify Conclusions The coastline of the Atlantic
Coast is 2,069 miles long. Approximately
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One half of 4 is
• 4 or 2.
of the
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coastline lies in New Hampshire. About how many
miles of the coastline lie in New Hampshire? Explain
how you estimated.
fifths, of 1%. 2,069 is about 2,000.
1% of 2,000 = 0.01 • 2,000 or 20
10% of 40 is 4.
32% is about 3 • 10%.
3 • 4 = 12
So, 32%and
of 43Estimation
is about 12.
2-2 Percent
You use about 12 muscles when you smile.
About 12 miles of coastline lie in New Hampshire.
28. Justify Conclusions The coastline of the Atlantic
Coast is 2,069 miles long. Approximately
of the
coastline lies in New Hampshire. About how many
miles of the coastline lie in New Hampshire? Explain
how you estimated.
29. The table shows the number of passes attempted and
the percent completed by the top quarterbacks in the
NFL for a recent season.
SOLUTION: Estimate
of 2,069.
is six tenths, or three fifths, of 1%. 2,069 is about 2,000.
1% of 2,000 = 0.01 • 2,000 or 20
About 12 miles of coastline lie in New Hampshire.
29. The table shows the number of passes attempted and
the percent completed by the top quarterbacks in the
NFL for a recent season.
a. Estimate the number of passes that Tom Brady
completed.
b. Is your estimate greater or less than the actual
number of passes he completed? Explain.
c. Without calculating, determine whether Tony
Romo or David Garrard completed more passes.
Justify your reasoning.
SOLUTION: a. Round 69% to 70% and 578 to 600. Then multiply
70%, or
, and 600.
So, Tom Brady completed about 420 passes.
a. Estimate the number of passes that Tom Brady
completed.
b. Is your estimate greater or less than the actual
number of passes he completed? Explain.
c. Without calculating, determine whether Tony
Romo or David Garrard completed more passes.
Justify your reasoning.
b. The estimate of 420 passes is greater than the
actual number of passes because the number of
passes and the percent were both rounded up.
c. Tony Romo completed 64% of 520 passes. David
Garrard completed 64% of 325 passes. Since 520 >
325, 64% of 520 must be greater than 64% of 325.
Therefore, Tony Romo completed more passes than
David Garrard.
SOLUTION: a. Round 69% to 70% and 578 to 600. Then multiply
70%, or
, and 600.
So, Tom Brady completed about 420 passes.
b. The estimate of 420 passes is greater than the
actual number of passes because the number of
passes and the percent were both rounded up.
c. Tony Romo completed 64% of 520 passes. David
Garrard completed 64% of 325 passes. Since 520 >
325, 64% of 520 must be greater than 64% of 325.
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Therefore, Tony Romo completed more passes than
David Garrard.
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