S k i l l
 i n
A R I T H M E T I C

Table of Contents | Home | Introduction

Lesson 3  Section 2

The Meaning of Percent

The student should first understand Section 1:  Multiplying and Dividing by Powers of 10.


 7.   What does "percent" mean?
 
  Percent is an abbreviation for the Latin per centum, which means for each 100.

Thus, 100% means 100 for each 100, which is to say, all.  100% of 12 is all of 12.

50% is another way of saying half, because 50% means 50 for each 100, which is half.  50% of 12 is 6.

Example 1.   Below are 100 squares, and 32 have been shaded.

What percent of the squares have been shaded?

Answer.   32% -- 32 for each 100.

When the percent is less than or equal to 100%, then we can say "out of" 100.  32% is 32 out of 100.  (But to say that 200% is 200 out of 100 makes no sense.  200% is 200 for each 100, which is to say, twice as much.)

Example 2.   100 people were surveyed, and 65 responded Yes.  What percent responded Yes?

Answer.   65% -- 65 out of 100.

Example 3.   In a class of 30 students, all 30 came to school by bus. What percent came to school by bus?

Answer.   100%.  100% means all.

(30 for each 30 is equivalent to 100 for each 100.)



 8.   How do we take 1% of a number?
 
1% of $200
 
  Divide it by 100.  For, 1% means 1 for each 100,
which is the hundredth part.

1% = 1 for each 100.

Examples.

1% of $200 is $2.00 Divide by 100:  Separate two decimal places.
 
1% of $250 is $2.50 Again, divide by 100:  Separate two decimal places.
 
1% of $6.00 is $.06     Move the point two places left.  Do not write the 0's that remain on the extreme right of the decimal:
 
  6.00 ÷ 100 = .0600 = .06
 
  (Lesson 2, Question 8.)
 
1% of $1,200 is $12.00      Divide by 100:  Separate two decimal places, or simply drop the two 0's.

Problem 1.   How much is 1% of $400?  How much is 2% of $400?  How much is 3%?  How much is 9%?

Answer.   1% of $400 is $4.00.   Separate two decimal places.

Now, 2% is twice as much as 1%.  Therefore 2% of $400 is $8.  3% is $12.  4% would be $16.  9%, therefore, is 9 × $4 = $36.

Problem 2.   How much is 8% of $600?

Answer.   Since 1% is $6.00, then 8% is 8 × $6.00 = $48.00.

Problem 3.   How much is 2% of $325?  How much is 3%?  4%?

Answer.   We can get everything from 1%, which is $3.25.

2%, therefore, is $6.50.

3% is $9.75.

And 4% is 4 × $3.25 = 4 × $3  +  4 × $.25 = $12 + $1 = $13.

These are problems that do not require a calculator. They should be done mentally!



 9.  How do we take 10% of a number?
 
10% of $600
 
  Divide it by 10.  For, 10% means 10 for each 100. Each 10 is a tenth part of 100.

Examples.

10% of $600 is $60. Divide by 10:  Take off one 0, or separate one decimal place.
10% of $625 is $62.50 Divide by 10.  Separate one decimal place:  $62.5
But we write money with two decimal places (cents).  Therefore we must add a 0 onto the right.
10% of $6.00 is $.60 Move the point one place left.  Again, we write money with two decimal places.

Problem.   How much is 20% of $80?  How much is 30%?  How much is 90%

Answer.   20% is twice as much as 10%.  Since 10% of $80 is $8, then 20% is 2 × $8 = $16.  30% is 3 × $8 = $24.  90% is 9 × $8 = $72.

The meaning of percent continues in Lesson 14 and Lesson 27.


 10.   How do we change a percent to a number?
 
24% = ?
 
  Divide by 100.

(This is often called changing a percent to a decimal.)

24% = .24     

Divide by 100 -- separate two decimal places.  For, 24% -- 24 for each 100 -- means 24 hundredths.

Division by 100 is indicated by the percent sign itself  %, with its division slash / and two 0's.

Here are more examples:

.24%   =    .0024   Divide by 100:  Move the decimal point two places left.
9%   =    .09   Divide by 100:  Mark off two decimal places.
   650%   =    6.5   Divide by 100:  Mark off two decimal places.
It is not necessary to write the 0 that remains on the right of the decimal.  650% = 6.50 = 6.5  
 
6.5%   =    .065   Divide by 100:  Move the decimal point two places left.

Strictly, a percent is not a number, it is a ratio (Lesson 27). Therefore we should speak rather of a number representing a percent. That becomes necessary only for certain written calculations.


 11.   How do we change a number to a percent?
 
  .24 =  ? %
 
  Multiply it by 100, and add the % sign.

Examples.

.24  =  24% Multiply by 100:  Move the point two places right.
 
2.4  =  240% Move the point two places right.
 
24  =  2400%   Multiply by 100:  Add on two 0's.
 
.024  =  2.4% Move the point two places right.

Number to a Percent

.24 = 24%

Percent to a Number


Please "turn" the page and do some Problems.

or

Continue on to the next Lesson.

Section 1 of this Lesson


Introduction | Home | Table of Contents


Please make a donation to keep TheMathPage online.
Even $1 will help.


Copyright © 2001-2007 Lawrence Spector

Questions or comments?

E-mail:  themathpage@nyc.rr.com