Percents
Percent means per hundred. Convert to a decimal and multiply, and use the original as the base for change.
The rules
- x% of y is (x/100)·y.
- Percent change = (new − old) / old × 100.
- To increase by 20%, multiply by 1.20. To decrease by 20%, multiply by 0.80.
- Successive changes multiply. They do not add.
Watch out: Using the wrong base for percent change. Always divide by the original.
Worked example
A jacket costs $85 after a 15% discount. What was the original price?
- The sale price is 85% of the original.
- 0.85x = 85, so x = 100.
Answer: $100
Try it yourself
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