Mental Math: Percent
12-1
Here are some percents that are equivalent to common fractions.
0
4
1
4
2
4
3
4
4
4
Study the pattern for these percents and common fractions.
1 0%
1
1
0
02 0%
1
2
0
or ^1
5
3 0%
1
3
0
04 0%
1
4
0
or
2
5
5 0%
1
5
0
or
1
2
06 0%
1
6
0
or
3
5
7 0%
1
7
0
08 0%
1
8
0
or
4
5
9 0%
1
9
0
10 0%
1
1
0
0
or
5
5
or 1
To find a percent of a number mentally,
use common fractions.
Find the value of n.
25% of 36n. 40% of 35n.
^14 of 36 n ^25 of 35 n
^14 36 9 ^25 35 14
So n9. So n14.
Find the value of the variable. Compute mentally.
1
5 of 30 6, so 20% of 30 n. 2. of 40 2, so 5% of 40 c.
2
5 of 30 12, so 40% of 30 a. 4. of 40 6, so 15% of 40 r.
3
20
1
20
Remember: “of”
means “times.”
Think
25%
1
4
Think
40%
2
5
1
9
1
7
0% 25% 50% 75% 100%
1.0
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