Percent of Quantity

Grade 6 · ratios · 84 practice problems · read aloud

🔊 Listen to this explanation

Percent of a Quantity 🧮

What is it and Why is it Useful?

A percent means "out of 100." Finding a percent of a quantity helps us figure out a part of a whole. We use this all the time in real life—like calculating sales tax, discounts during a sale, or tips at a restaurant!

How to Solve: Step-by-Step

  1. Convert the percent to a decimal. (Move the decimal point two places to the left, or divide by 100).
  2. Multiply the decimal by the original quantity.
  3. That's your answer! You've found the percent of the quantity.

Visual Examples

Example 1: What is 20% of 80?

  1. Convert: 20% = 20 ÷ 100 = 0.20
  2. Multiply: 0.20 × 80 = 16

✅ Answer: 16

Example 2: What is 5% of 300?

  1. Convert: 5% = 5 ÷ 100 = 0.05
  2. Multiply: 0.05 × 300 = 15

✅ Answer: 15

Common Mistakes to Avoid 🚫

Forgetting to Convert: Don't just multiply the percent number by the quantity! You MUST convert it to a decimal first. 20% of 80 is NOT 20 × 80 = 1600.

Misplacing the Decimal: When moving the decimal point two places, double-check your work. For 5%, it's 0.05, not 0.5.

Tips & Tricks

Memory Aid: Think "Divide and Multiply" — Divide the percent by 100, then Multiply by the number.

Shortcut for 10%: To find 10% of any number, just move the decimal point one place to the left. Then you can use that to find other percents (e.g., 20% is just 2 × 10%).

How to Practice

  • Start with simple numbers: Find 10%, 25%, and 50% of different quantities.
  • Create your own real-world problems. "If a video game costs $60 and is 15% off, how much money do I save?"
  • Use online math games or flashcards to build speed and accuracy.

Practice problems

6 of the 84, worked through step by step — try them before opening the answer.

1 25% of 480 = ?

Hint: Remember that percent means 'per hundred.' Think about how you can convert the percentage to a decimal or fraction to make the calculation easier.

Show the answer

Answer: 120

  1. Understand that "percent" means "per hundred". So 25% means 25 per hundred, which can be written as 25/100.
  2. "Of" in mathematics usually means multiplication. So 25% of 480 means (25/100) × 480.
  3. Simplify 25/100. 25/100 = 1/4.
  4. Now compute (1/4) × 480. This is the same as 480 ÷ 4.
  5. 480 ÷ 4 = 120.
  6. Therefore, 25% of 480 is 120. Final answer: 120

We are asked to find 25% of 480.

2 35% of 840 = ?

Hint: Remember that finding a percentage of a number involves converting the percentage to a decimal and then multiplying by the quantity.

Show the answer

Answer: 294

  1. Understand that "percent" means "per hundred." So 35% means 35 per hundred, which can be written as 35/100.
  2. "Of" in mathematics usually means multiplication. So 35% of 840 means: (35/100) × 840
  3. Simplify the calculation. We can first multiply 35 by 840, then divide by 100. 35 × 840 = ? Break it down: 35 × 800 = 28,000 35 × 40 = 1,400 Add them: 28,000 + 1,400 = 29,400
  4. Now divide by 100. 29,400 ÷ 100 = 294
  5. Final answer. 35% of 840 = 294 We can check: 10% of 840 is 84, so 30% is 3 × 84 = 252, and 5% is half of 84, which is 42. Then 252 + 42 = 294.

We want to calculate 35% of 840.

3 45% of 280 = ?

Hint: Remember that percentage means 'per hundred.' To find a percentage of a quantity, you can convert the percentage to a decimal and then multiply by the quantity.

Show the answer

Answer: 126

  1. Understand that "percent" means "per hundred". So 45% means 45 per 100, which can be written as 45/100.
  2. "Of" in mathematics usually means multiplication. So 45% of 280 means (45/100) × 280.
  3. Write the multiplication: (45/100) × 280
  4. Simplify the calculation. We can multiply 45 by 280 first, then divide by 100. 45 × 280 = 45 × (200 + 80) = (45 × 200) + (45 × 80) = 9000 + 3600 = 12600
  5. Now divide by 100: 12600 ÷ 100 = 126 Alternatively, you could simplify before multiplying: (45/100) × 280 = 45 × (280/100) 280/100 = 2.8 45 × 2.8 = 45 × (2 + 0.8) = 90 + 36 = 126 Both methods give the same result. Final answer: 126

We are asked to find 45% of 280.

4 25% of 840 = ?

Hint: Remember that percentage means 'per hundred'. For example, 10% of 300 would be 30.

Show the answer

Answer: 210

  1. Understand that "percent" means "per hundred." So 25% means 25 per hundred, which can be written as 25/100.
  2. "Of" in mathematics usually means multiplication. So 25% of 840 means: (25/100) × 840
  3. Simplify the fraction 25/100. 25/100 = 1/4, because both numerator and denominator can be divided by 25.
  4. Now the problem becomes: (1/4) × 840
  5. Multiply 1/4 by 840. This is the same as dividing 840 by 4.
  6. 840 ÷ 4 = 210.
  7. Therefore, 25% of 840 is 210. Final answer: 210

We are asked to find 25% of 840.

5 25% of 320 = ?

Hint: Remember that percentage means 'per hundred.' Think about how to find a fraction of a quantity.

Show the answer

Answer: 80

  1. Understand that "percent" means "per hundred". So 25% means 25 per hundred, which can be written as 25/100.
  2. "Of" in mathematics usually means multiplication. So 25% of 320 means: (25/100) × 320
  3. Simplify 25/100. 25/100 = 1/4 (since both numerator and denominator are divisible by 25).
  4. Now compute (1/4) × 320. This is the same as 320 ÷ 4.
  5. 320 ÷ 4 = 80.
  6. Therefore, 25% of 320 is 80. Final answer: 80

We are asked to find 25% of 320.

6 35% of 720 = ?

Hint: Remember that percentage means 'per hundred' - think about how to convert the percentage to a decimal before multiplying

Show the answer

Answer: 252

  1. Convert 35% to a decimal by dividing by 100: 35 ÷ 100 = 0.35
  2. Multiply the decimal by the total quantity: 0.35 × 720
  3. Calculate 0.35 × 720 = 252

The answer is 252.

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