The Percentage of Change

April 30, 2008

From About.com: Mathematics:

Let's say you weighed 180 pounds and lost 30 pounds and wondered what percent of your body weight you lost. Or let's say you saw a great sale for 25% off and want to quickly calculate it, this mini tutorial shows you how. Not only that, learn some quick estimation skills and do the percentage in your head on the fly!

Finding the percent of change is using the ratio of the amount of change to the original amount. The increased amount is really the percent of increase. If the amount decreases then the percent of the change is the percent of the decrease which will be a negative.

The first question to ask yourself when finding the percent of change is: Is it an increase or a decrease?

Let's try a problem:

175 to 200 -- We have an increase of 25 and subtracted to find out the amount of change.

Next, we will divide the amount of change by our original amount.

25 ÷ 200 = 0.125

Now we need to change the decimal to a percent by multiplying 1.125 by 100:

12.5%

We now know that the percentage of change which in this case is an increase from 175 to 200 is 12.5%

Let's try one that is a decrease:

Let's say I weight 150 pounds and I lost 25 pounds and want to know my percentage of weight loss.

First, I subtract 25 from 150 to find the amount of change which is 25.

I then divide the amount of change by the original amount:

25 ÷ 150 = 0.166

Now I will multiply 0.166 by 100 to obtain my percentage of change:

0.166 x 100 = 16.6%

Therefore, I have lost 16.6% of my body weight.

Understanding the percentage of change concept is important for crowd attendance, points, scores, money, weight, depreciation and appreciation concepts etc.

Then again, if you want to take the short cut, here is a percent calculator that eliminates the mental or paper/pencil calculation.