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WHAT PERCENT?

Lesson 29  Section 2


We have seen:

To change a number to a percent, multiply it by 100, and add the % sign.

(Lesson 3.)

Example 1.

.125  =  12.5%    To multiply by 100, move the point two places right.
 
2.6  =  260%    Move the point two places right.
 
8  =  800%    Multiply by 100:   Add on two 0's.

Example 2.   7 out of 12 people voted Yes.  What percent voted Yes?

   Solution.   Express 7 out of 12 as the fraction   7 
12		  , and multiply by 100.

Write

 7 
12		  × 100  =  700
 12		  = 700 ÷ 12

"12 goes into 70 five (5) times (60) with 10 left over."  (Lesson 11.)

"12 goes into 100 eight (8) times (96) with 4 left over."

 The fraction   4 
12		  reduces to  1
3		 .  Therefore,
7 out of 12 = 58 1
3		 %.

Always:

A out of B =  A
B		  × 100%

To do this problem with a calculator, press

7 ÷ 12 %

See

 58.3333333 

This is approximately 58.3%.

With a calculator, dividing approximates the fraction as a decimal. (Lesson 23.) The % key multiplies it by 100.
 3.   What is a general method for finding the Percent?
 
  Write the fraction that has the Base as the denominator and the Amount as the numerator, and express that fraction as a percent.
Amount
   Base		  = ? %

Certain fractions come up frequently, and the student should know their percent equivalents.  See Problem 18.

Example 3.   21 is what percent of 15?

Solution.   First, note that 21 is more than 15. Therefore it will be more than 100% of 15. (Lesson 16.)  On reducing and expressing the improper fraction as a mixed number:

21
15		   =   7
5		   =  1 2
5		 .
The percent will be 1 2
5		  × 100%. .
1 × 100% = 100%.    2
5		  × 100% = 40%.

21 is 140% of 15.


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