Notes on Calculating Percent

By Proportion

There are three basic percent problems:

1)                 What is          15%               of 180?

2)                 12 is          what percent      of 95?

3)                 60 is                40%             of what number?

We break these problems into three parts:   Is,  Of,  and percent and we use a Magic Formula!

Just plug in the numbers and solve by proportion!

1)     What is  15%  of 180?

We don’t know the “is”, so we use a variable, n.  The “of” is 180.  So using the formula

we place, since the percent is 15%.  Then we solve it like a proportion,

100n = 15∙180

100n = 2700

100                 100

n = 27     so we can answer: 27 is 15% of 180.

2) 12 is  what percent   of 95?

In this problem, 12 is the “is”, 95 is the “of” and n is the percent.  So plug it in!

we place and solve by proportion:

95n = 1200

95                    95

12 is about 13% of 95

3) 60 is  40%  of what number?

In this problem, 60 is the “is”, n is the “of” and 40 is the percent. So plug it in!

we place and solve by proportion:

6000 = 40n

40     40

150  =  n

So we answer 60 is 40% of 150.

Unfortunately not all percent problems are worded so easily: Link here to see other wording: