Percent change is often used in news articles to show how a statistic has increased -- you might see a headline that says that the price of oil has increased by 5 percent. To increase a number by a percentage, first find that percentage of the number, then add it to the original number.
Convert the Percent to a Decimal
Any percent can be represented by a decimal number -- 50 percent, for instance, is 0.5. To convert a percent to a decimal number, you take that percent move the decimal place two points to the left. For example, to convert 75 percent, you take the number 75 and move the decimal two to the left, getting 0.75.
Say that your farm grew 78 pounds of potatoes last year, and this year it grew 15 percent more than last year. You'd first convert the additional percentage of 15 to a decimal, getting 0.15.
Determine the Increase
You can now find how much the weight of your potatoes has increased this year. To determine the amount of increase, multiply the decimal of the percentage by the original total. Your potato weight increased by 15 percent of 78 pounds. So the increase is equal to .15 multiplied by 78:
0.15 x 78 pounds = 11.7 pounds
So you 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. Your original total was 78 pounds, and your increase was 11.7 pounds, so the new total is:
78 pounds + 11.7 pounds = 89.7 pounds.
So you produced 89.7 pounds of potatoes this year.
Note that if your total was decreasing by a percentage, you would subtract this number instead. So if your potato weight had gone down by 15 percent since last year, you would have produced 78 minus 11.7 pounds, or 66.3 pounds this year.