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Use your own numbers after reviewing the example below.
Quick answer
Divide the known result by the percentage written as a decimal. If 45 is 30% of a number, calculate 45 ÷ 0.30 = 150.
Formula or method
Original whole = known part ÷ percentage as a decimal
Step-by-step
- Convert the percentage to decimal form.
- Divide the known amount by that decimal.
- Multiply the answer by the percentage to check it.
Worked example
45 is 30% of what number? 30% = 0.30, so 45 ÷ 0.30 = 150. Check: 30% of 150 = 45.
How to interpret the result
This method applies when the known amount is a stated percentage of the original whole. Reverse discount problems may require a different setup because the final price represents 100% minus the discount percentage.
Common mistakes
- Multiplying when you need to divide.
- Using 30 instead of 0.30.
- Confusing “30% of” with “30% off.”
Frequently asked questions
If 24 is 20% of a number, what is the number?
24 ÷ 0.20 = 120.
How do I reverse a 20% discount?
If the sale price is 80% of the original, divide the sale price by 0.80.
Why do I convert percent to decimal?
Percent means per 100, so 30% = 30/100 = 0.30.