All SAT GuidesStudy Guide
Percents and Percent Change
A percent is a proportion of a specific base. Identify that base before calculating discounts, increases, decreases or comparisons.
Key Rules
- Convert p% to p/100.
- Percent change equals change divided by the original amount, then multiplied by 100%.
- A decrease of r as a decimal multiplies the original by 1 − r.
Common Mistakes to Avoid
- Dividing by the new amount when calculating percent change.
- Assuming an increase and an equal percentage decrease undo each other.
SAT Strategy Tips
- →Write “percent of what?” beside the problem.
- →For successive changes, multiply the factors in sequence.
Example Question
A jacket originally costs 80 dollars. It is discounted by 25%. What is the sale price?