Pre-Algebra Chapter 6 - Ramsey School District

Finding Percents Mentally
• Compute mentally with percents.
• Estimate with percents.
is estimation used when determining sale prices?
A sporting goods store is having a
sale in which all merchandise is on sale
at half off. A few regularly priced items
are shown at the right.
a. What is the sale price of each item?
b. What percent represents half off?
c. Suppose the items are on sale for
25% off. Explain how you would
determine the sale price.
$44
$68
$37
$15
FIND PERCENTS OF A NUMBER MENTALLY When working with
common percents like 10%, 25%, 40%, and 50%, it may be helpful to use the
fraction form of the percent. A few percent-fraction equivalents are shown.
0% 12 1 % 25% 40% 50% 66 2 % 75% 87 1 % 100%
2
3
2
0
1
8
1
4
2
5
1
2
2
3
3
4
7
8
1
Some percents are used more frequently than others. So, it is a good idea to be
familiar with these percents and their equivalent fractions.
Percent-Fraction Equivalents
20% 1 5 10% 1
25% 1 10
4 121 2 % 1 8 162 3 % 1 6
40% 2 5 30% 3
50% 1 10
2 371 2 % 3 8 331 3 % 1 3
60% 3 5 70% 7
75% 3 10
4 621 2 % 5 8 662 3 % 2 3
80% 4 5 90% 9
87 1 10
2 % 7 8 831 3 % 5 6
Study Tip
Look Back
To review multiplying
fractions, see Lesson 5-3.
Example 1
Find Percent of a Number Mentally
Find the percent of each number mentally.
a. 50% of 32
50% of 32 1 2 of 32 Think: 50% 1 2 .
16 Think: 1 of 32 is 16.
2
So, 50% of 32 is 16.
Lesson 6-6 Finding Percents Mentally 293