Finding a Basic Percent

Find 20% of 150.

Convert percent to decimal: $20\% = 20 \div 100 = 0.20$ = 0.20

Multiply by the number: $150 \times 0.20$ = 30

State the answer: $20\%$ of $150$ equals $30$ = 30

Answer: 20% of 150 is 30

Calculating a Discount

A 45 dollar sweater is on sale for 20% off. How much do you save?

Identify the percent and number: Percent = 20%, Number = 45 = 20% of 45

Convert percent to decimal: $20\% = 0.20$ = 0.20

Multiply to find savings: $45 \times 0.20 = 9$ = 9 dollars

State the answer: You save 9 dollars on the sweater = 9 dollars saved

Answer: You save 9 dollars. The sale price is 36 dollars.

Using the Fraction Method

Find 75% of 240.

Convert percent to fraction: $75\% = \frac{75}{100} = \frac{3}{4}$ = 3/4

Multiply by the number: $240 \times \frac{3}{4} = \frac{240 \times 3}{4} = \frac{720}{4}$ = 720/4

Simplify the result: $\frac{720}{4} = 180$ = 180

Answer: 75% of 240 is 180

Finding a Small Percent

Find 8% of 350.

Convert percent to decimal: $8\% = 8 \div 100 = 0.08$ = 0.08

Multiply by the number: $350 \times 0.08$ = 28

Check another way: $1\%$ of $350 = 3.5$, so $8\% = 8 \times 3.5 = 28$ = 28 is correct

Answer: 8% of 350 is 28

Mistake: Forgetting to convert percent to decimal (calculating $20 \times 150 = 3000$ instead of $0.20 \times 150 = 30$)

Why: The percent symbol means 'per hundred'. 20% is 20 per 100, which equals 0.20, not 20.

Correct: Always divide the percent by 100 first: $20\% = 0.20$, then multiply.

Mistake: Moving the decimal point only one place (writing 5% as 0.5 instead of 0.05)

Why: Percent means 'divide by 100', so the decimal point moves two places LEFT, not one. 0.5 would be 50%.

Correct: $5\% = 0.05$ and $20\% = 0.20$ (the decimal point moves two places LEFT)

Mistake: Confusing 'percent of' with 'percent off'

Why: '20% of 100' means find 20 (the answer). '20% off 100' means subtract 20 to get 80 (the final price).

Correct: For discounts, first find the percent, then subtract from the original.

Shopping Discounts

Stores use percentages to show how much you save during sales.

An 80 dollar jacket is 25% off. Savings: $80 \times 0.25 = 20$ dollars. Sale price: $80 - 20 = 60$ dollars.

Restaurant Tips

Calculating tips is a common use of percentages.

On a 40 dollar meal, a 15% tip is $40 \times 0.15 = 6$ dollars.

Test Scores

Teachers often tell you what percent you scored on a test.

If a test has 40 questions and you need 80% to pass, you need $40 \times 0.80 = 32$ correct answers.

Q: What is the fastest way to find 10% of any number?

A: Just move the decimal point one place to the left! 10% of 250 = 25.0 = 25. This works because dividing by 10 moves the decimal left.

Q: How do I find 15% quickly?

A: Find 10% (divide by 10), then find 5% (half of 10%), and add them together. For 15% of 80: 10% = 8, 5% = 4, so 15% = 12.

Q: Is finding 25% of a number the same as dividing by 4?

A: Yes! 25% = 25/100 = 1/4. So 25% of 80 = 80/4 = 20.