One of the most confusing and difficult skills to master,
for many students, is the idea of percent.
And yet the concept of percent is all around
us in our everyday life.
Sales tax, income tax, discounts, interest rates,
political polls, games of chance, even weather forecasts
(there's a 30% chance of rain), are just some
of the many examples of the widespread
use of percents in the real world.
So why is it so difficult for the majority
of students (and adults!) to master the rules of percent?
A big part of the reason lies in the fact that
although everyone knows that percent
means "out of 100", very, few "real life"
situations deal with 100 of anything!
For example, are there 100 kids in your class?  Probably not. 
So what does it mean when the teacher says
that 20% of your class is buying the school lunch today?
Or how about this one, does every test you take have exactly 100
questions on it? Again, probably not....but your grade might very well be written as a percent....So what's going on here? 
How can we take away some of the confusion that
percent always seems to create?
 

Before we look at some examples let's look at the following chart.
Notice that for every percent there is an equivalent
fraction and decimal number.  We will rely heavily on the
fractional equivalents when we do the estimation in the examples.

EXAMPLE 1:
There are 48 cars in the faculty parking lot at Tom's school.
19 of them are silver.  About what percent of the cars are silver?
Solution:
Because we are estimating the answer, the first thing to do is
to round the numbers in the problem into an easier to use amount.
48 cars ≈ 50 cars
19 silver cars ≈ 20 silver cars
The "rounded" problem becomes 20 out of 50 are silver.
If we make that into a fraction 20/50,
and reduce to lowest terms we get 2/5
Look at the chart....
2/5 is 40%....
So...a good estimation of the percentage of silver cars
in the parking lot is 40%

Remember...although all of the steps were written out
to help you follow along with the process, after you have done
several of these types of problems you will should to perform these very
simple calculations in your head.  In fact, as we go through
the next examples, try to make the estimations
on your own before looking at the answer.

Example 2:
There are 23 kids in the class, and
18 of them are right handed.
About what percent of the class is right handed?
(try it on your own before looking at the solution)
Solution:
First, round off the numbers to numbers
that are easier to work with.
23 kids ≈ 25 kids
18 right handed kids ≈ 20 right handed kids
The "rounded" problem becomes 20 out of 25 kids are right handed
As a fraction that is 20/25
Reduce the fraction...20/25 = 4/5
Look in the chart...
4/5 = 80%
A good estimate of the percentage of kids in the
class who are right handed is 80%
Did you get that on your own ???

Let's try one more...
Example 3:
Mr. Smith was running for Mayor.
In the election, 14,762 people voted.
Of those,9127 voted for Mr. Smith.
Approximately, what percent of the vote did he receive?
round the numbers:
14,762 ≈ 15,000
9,127 ≈ 9,000
Fraction is:
 9000/15000
Reduce the fraction:
9000/15000 = 3/5
Look in the chart:
3/5 = 60%
Mr. Smith received approximately 60% of the vote.

How did you do on this one??
You see how easy this can be?  And it really is this easy
if, you round off to numbers that are easy to work with.
And isn't that what rounding off is supposed to do?
So the next time you are faced with calculating a percent...
and close enough... is good enough,
(and in real life that's the way it will be)
use the method described in this lesson.

Now click below to practice some more on your own.

Click Here