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Percent Formula

Part = Percent × Whole

What is 12% of 25?
Part = .12 × 25

15 is 3% of what number?
15 = .03 × Whole

45 is what percent of 9?
45 = Percent × 9


Percent Increase and Decrease

To increase a number by a percent, add the percent to 100%, convert to a decimal, and multiply.

Increase 40 by 25%: add 25% to 100%, covert 125% to 1.25, and multiply by 40. 1.25 × 40 = 50


Finding the Original Whole

TO find the original whole before a percent increase or decrease, set up an equation. Think of a 15% increase over x as 1.15x

After a 5% increase, the population was 59,346. What was the population before the increase? → 1.05x = 59,346


Combined Percent Increase and Decrease

To determine the combined effect of multiple percents increase and/or decrease, start with 100.

A price went up 10% one year, and the new price went up 20% the next year. What was the combined percent increase?

Setup: First year: 100 + (10% of 100) = 110. Second year: 110 + (20% of 110) = 132. That is a combined 32% increase.