6th Grade Math Textbook, Progress

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. 
   
   1
   5
   of 30 6, so 20% of 30 n. 2. of 40 2, so 5% of 40 c.


2. 
   
   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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