Percentages
Percent means 'per hundred.' 45% = 45/100 = 0.45. Percentages are everywhere: sales tax, discounts, test scores, statistics. The three core problems are: find the percent of a number, find what percent one number is of another, and find the whole when you know a percent.
Key Concepts
Finding a Percent of a Number
'What is 30% of 80?' Convert: 30% = 0.30. Multiply: 0.30 × 80 = 24. Shortcut: 10% of 80 = 8, so 30% = 3 × 8 = 24. Always check with 10% and 50% estimates first.
Percent Increase and Decrease
A shirt costs $40 and goes on sale for 25% off. Discount = 25% × $40 = $10. Sale price = $40 − $10 = $30. Or: 100% − 25% = 75% of original. $40 × 0.75 = $30. Tax works the same way: $30 + 8% tax = $30 × 1.08 = $32.40.
Finding What Percent
15 is what percent of 60? Set up: 15/60 = 0.25 = 25%. Divide part by whole, multiply by 100. Use this for test scores: 42 out of 50 correct = 42/50 = 0.84 = 84%.
🆕 Percent Calculator
Solve all three types of percent problems. See the work shown!
✅ Check Your Understanding
1. What is 20% of 150?
2. A $60 item is 25% off. What is the sale price?
3. 18 out of 24 correct. What percent is that?