How to Solve Percent Problems: Examples and Free Practice

Choose the right percent calculation

A percent is a rate per 100. Use part = decimal rate × whole. First decide which quantity is missing; then choose the calculation below. For example, 20% means 20 ÷ 100 = 0.20.

How to identify the whole

The whole is the amount treated as 100%. In “30% of 150,” 150 is the whole. In “25 is 20% of what number?” the whole is unknown. Do not automatically choose the smaller number.

Finding a sale price: A $60 jacket is discounted by 25%. The discount is 0.25 × $60 = $15. Subtract the discount: $60 − $15 = $45. The discount amount and the final price answer different questions.

Finding an original price: A jacket costs $45 after a 25% discount. The sale price is 75% of the original, so the original price is $45 ÷ 0.75 = $60. Dividing by 0.25 would find a different quantity.

Try six percent problems

Identify the missing quantity before calculating. The answers below are for these public lesson exercises.

1. What is 15% of 80?
2. 12 is what percent of 48?
3. 36 is 90% of what number?
4. What is 40% of 250?
5. 7 is what percent of 35?
6. 18 is 60% of what number?

Check your method

A percent below 100% gives a part smaller than a positive whole; a percent above 100% gives a part larger than that whole. For example, 125% of 80 is 1.25 × 80 = 100. A percent is not restricted to values below 100%.

You can also set up part ÷ whole = percent ÷ 100. Keep the part and whole in the same order on each side. If the whole is zero, “what percent?” is undefined because division by zero is not defined.

This skill connects to Grade 6 ratio and percent reasoning, including finding a part or an unknown whole. Use the practice tool above for more questions and explanations. For fraction, decimal and ratio review, visit the free Pre-Algebra learning center.