Percent Proportion

We ended last week by discussing the Percent Proportion.  The percent proportion is a tool you can use for all percent problems.  It is

   %    =   part  
 100       whole

The percent sign, part, and whole are all places where you plug in information from a problem.

There are 3 types of percent problems.  Problems where the % is missing, the part is missing, and the whole amount is missing.  Here are 3 examples:

What is 25% of 80?

20 is what percent of 80?

20 is 25% of what number?

Each of these problems can be solved by using the percent proportion.

Problem 1   25   =    x         Problem 2    x    =   20         Problem 3    25   =   20  
                  100       80                          100       80                           100        x

To solve each problem you cross multiply and divide by the value with the variable.

Problem 1    25   =    x   
                   100       80

                 100 x  =  25 (80)
                 100x  =  2000
                  100        100

                       x = 20

All 3 forms of the percent problems are solved the same way.

Most problems don't look like the examples.  They look more like this one:

The Incredible Chocolate Chip Company has discovered that 36 out of 400
chocolate chip cookies do not contain enough chocolate chips. What percent of
the chocolate chip cookies do not have enough chips?

In this problem we are looking for the percent so it will be like problem 2.

   x    =   36  
 100      400

400x = 3600
400       400

   x = 9%

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