Percent concept, conversions, calculations
Middle School Bridge • 6-8
When a store advertises "30% off," you instantly know you are saving a meaningful chunk of the price. When a weather forecast says "80% chance of rain," you grab an umbrella. Percentages are everywhere in daily life because they provide a universal way to express parts of a whole using 100 as the base.
The word percent comes from the Latin per centum, meaning "per hundred." A percentage is simply a fraction with a denominator of 100.
| Conversion | Method | Example |
|---|---|---|
| Percent to Decimal | Divide by 100 (move decimal 2 left) | 75% = 0.75 |
| Decimal to Percent | Multiply by 100 (move decimal 2 right) | 0.4 = 40% |
| Percent to Fraction | Write over 100, simplify | 60% = 60⁄100 = 3⁄5 |
| Fraction to Percent | Divide, then multiply by 100 | 3⁄8 = 0.375 = 37.5% |
What is 20% of 85?
20% of 85 is 17.
You scored 18 out of 24 on a quiz. What percent is that?
You scored 75%.
15% of what number is 36?
The number is 240.
Every percent question is one of three types: (1) find the part (percent × whole), (2) find the percent (part ÷ whole × 100), or (3) find the whole (part ÷ percent as decimal). Identify which piece is missing and use the appropriate formula.
Do not confuse moving the decimal point left versus right. To go from percent to decimal, move the decimal left two places (making the number smaller). To go from decimal to percent, move it right two places (making the number larger). A quick sanity check: 50% should equal 0.5, not 5.0.
1. Convert 0.08 to a percent.
0.08 × 100 = 8%.
2. What is 35% of 200?
0.35 × 200 = 70.
3. Express 5⁄8 as a percent.
5 ÷ 8 = 0.625. 0.625 × 100 = 62.5%.
4. A shirt originally costs $40. It is on sale for 25% off. What is the sale price?
Discount = 0.25 × 40 = $10. Sale price = 40 − 10 = $30.
5. 12 is 60% of what number?
n = 12 ÷ 0.60 = 20.
A percent is a ratio out of 100. Convert between percents, decimals, and fractions by multiplying or dividing by 100. The three core percent calculations are finding the part, finding the percent, and finding the whole. Use the formula: Part = Percent (as decimal) × Whole, and rearrange as needed.