The percentage change is often used in news articles to show how a statistic has increased: you may see a headline that says the price of oil increased by 5 percent. To increase a number by a percentage, first find that percentage of the number and then add it to the original number.

**Convert the percentage to decimal**

Any percentage can be represented by a decimal number: 50 percent, for example, is 0.5. To convert a percentage to a decimal number, take that percentage move the decimal place two points to the left. For example, to convert 75 percent, take the number 75 and move the decimal two to the left, getting 0.75.

Let’s say your farm grew 78 pounds of potatoes last year, and this year it grew 15 percent more than last year. First I would convert the additional percentage of 15 to a decimal, getting 0.15.

**Determine the increase**

Now you can find how much the weight of your potatoes has increased this year. To determine the amount of increase, multiply the percentage decimal by the original total. His potato weight increased by 15 percent from 78 pounds. Then the increase is equal to .15 multiplied by 78:

0.15 x 78 pounds = 11.7 pounds

So he produced an additional 11.7 pounds this year.

**Add the increase**

Add the increase to your original total to find the total after the percentage increase. His original total was 78 pounds, and his increase was 11.7 pounds, so the new total is:

78 pounds + 11.7 pounds = 89.7 pounds.

So he produced 89.7 pounds of potatoes this year.

Keep in mind that if your total decreased by a percentage, you would subtract this number instead. So, if your potato weight dropped 15 percent from last year, it would have produced 78 minus 11.7 pounds, or 66.3 pounds this year.