2.2 Percent and Estimation
Objective:​ to estimate percents using fractions and decimals
★ Sometimes an exact answer is not needed when using
percents. One way to estimate the percent of a number is
to use a fraction.
a)
Estimate 42% of 120
42% ≈ 25
2
5
• 120 = 48
so, 42% of 120 ≈ 48
★ Another method for estimating the percent of a number is
first to find 10% of the number and then multiply.
b) Dante plans to put 80% of his paycheck into a savings
account and spend the other 20%. His paycheck this
week was $295. About how much money will he put into
his savings account?
$295 ≈ $300
and 10% of $300 is 30
30 × 8 = 240
so, 80% of 295 is about 240
★ When the percent is greater than 100, the estimate will
always be greater than the number.
c)
Estimate 174% of 200
174% is about 175%
175% of 200 = 100% of 200 + 75% of 200
= (1 • 200) + ( 34 • 200)
= 200 + 150
so, 174% of 200 is about 350
d)
298% of 45
e)
347% of 80
f) A county receives 34 % of a state sales tax. About how
much money would the county receive from the sale of a
computer that costs $1,020?
Guided practice: p.114, #1 - 7 all
HW: p. 115, #1- 12
Guided practice:
1. 12 • 10 = 5 ; 0.1 • 10 = 1 and 5x1=5
2. 45 • 500 = 400 ; 0.1 · 500 = 50 and 8 · 50 = 400
3. (1 · 70) + ( 12 · 70) = 105
4. 0.01 · 80 = 0.8 and 12 · 0.8 = 0.4
5. 48 teenagers; 35 · 80 = 48 ; 0.1x80=8 and 6x8=48
6. 160,000 acres; 0.01 x 20,000,000=200,000 and 45 of
200,000 = 160,000
7. Choose a multiple of 10 to represent the percent such as
20% for 22%. You can also round the number. Then multiply
the percent and number.
Examples:
d.
e.
f.
135,
280,
$7.50;
3 • 45 = 135
3 12 • 80 = 280
0.01 • 1,000 = 10 and
3
4
• 10 = 7 12