How to Calculate Percentages Easily: Perfect for NSW Students

Percentages are everywhere — in discounts, test scores, interest rates, and data comparisons. This guide helps NSW students understand what percentages mean, how to calculate them, and how to use them in practical maths problems.
Calculate Percentages Easily with Aussie Math Tutor NSW

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Interactive maths practice

Percentages Practice Test

Build confidence one level at a time. Start with percentage, decimal and fraction conversions, then progress through percentage calculations, discounts, GST, reverse percentages and compound changes.

  • 3 progressive levels
  • 30 practice questions
  • Instant answer checks
  • Hints and full working
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Level 1 Percentage Conversions 10 questions · Foundation 0/10

Tip: Include the % sign for percentage answers. Write decimals as plain decimals and fractions in simplest form using a/b.
  1. Convert 0.25 to a percentage.

    View hint and full working

    Hint: Multiply the decimal by 100 and add the percent sign.

    Working
    0.25 × 100 = 25
    Therefore, 0.25 = 25%.
    Answer: 25%
  2. Convert 3/5 to a percentage.

    View hint and full working

    Hint: Convert the fraction to a decimal, then multiply by 100.

    Working
    3 ÷ 5 = 0.6
    0.6 × 100% = 60%
    Answer: 60%
  3. Convert 45% to a decimal.

    View hint and full working

    Hint: Divide the percentage by 100.

    Working
    45% = 45 ÷ 100
    = 0.45
    Answer: 0.45
  4. Convert 7/8 to a percentage.

    View hint and full working

    Hint: Divide 7 by 8, then multiply by 100.

    Working
    7 ÷ 8 = 0.875
    0.875 × 100% = 87.5%
    Answer: 87.5%
  5. Convert 0.045 to a percentage.

    View hint and full working

    Hint: Multiply the decimal by 100 and add the percent sign.

    Working
    0.045 × 100% = 4.5%
    Answer: 4.5%
  6. Convert 35% to a fraction in simplest form.

    View hint and full working

    Hint: Write 35% as 35/100 and simplify.

    Working
    35% = 35/100
    35/100 ÷ 5/5 = 7/20
    Answer: 7/20
  7. Convert 2.5% to a decimal.

    View hint and full working

    Hint: Divide the percentage by 100.

    Working
    2.5% = 2.5 ÷ 100
    = 0.025
    Answer: 0.025
  8. Convert 9/20 to a percentage.

    View hint and full working

    Hint: Convert the fraction to a decimal, then multiply by 100.

    Working
    9 ÷ 20 = 0.45
    0.45 × 100% = 45%
    Answer: 45%
  9. Convert 140% to a fraction in simplest form.

    View hint and full working

    Hint: Write 140% as 140/100 and simplify.

    Working
    140% = 140/100
    = 14/10
    = 7/5
    Answer: 7/5
  10. Convert 3/4% to a decimal.

    View hint and full working

    Hint: First convert 3/4% to 0.75%, then divide by 100.

    Working
    3/4% = 0.75%
    0.75 ÷ 100 = 0.0075
    Answer: 0.0075

Level 2 Percentage Word Problems — Medium 10 questions · Core skills 0/10

Tip: Identify the original amount, the percentage and whether the question asks for a part, a new value or a percentage change.
  1. Find 15% of 80.

    View hint and full working

    Hint: Change 15% to 0.15 and multiply by 80.

    Working
    15% of 80 = 0.15 × 80
    = 12
    Answer: 12
  2. Find 20% of 150.

    View hint and full working

    Hint: Change 20% to 0.20 and multiply by 150.

    Working
    20% of 150 = 0.20 × 150
    = 30
    Answer: 30
  3. 18 is what percentage of 60?

    View hint and full working

    Hint: Divide the part by the whole, then multiply by 100.

    Working
    18 ÷ 60 = 0.3
    0.3 × 100% = 30%
    Answer: 30%
  4. Increase 250 by 12%.

    View hint and full working

    Hint: Multiply the original value by 1.12.

    Working
    250 × (1 + 0.12)
    = 250 × 1.12
    = 280
    Answer: 280
  5. Decrease 90 by 15%.

    View hint and full working

    Hint: Multiply the original value by 0.85.

    Working
    90 × (1 − 0.15)
    = 90 × 0.85
    = 76.5
    Answer: 76.5
  6. After a 10% discount, what is the new price of $50? Enter the number only.

    View hint and full working

    Hint: A 10% discount means paying 90% of the original price.

    Working
    50 × 0.90
    = 45
    Answer: 45
  7. Add 10% GST to $120. What is the GST amount? Enter the number only.

    View hint and full working

    Hint: The GST amount is 10% of $120.

    Working
    0.10 × 120
    = 12
    Answer: 12
  8. After a 20% discount, the price is $80. What was the original price? Enter the number only.

    View hint and full working

    Hint: After a 20% discount, 80% of the original price remains.

    Working
    Let the original price be x.
    0.80x = 80
    x = 80 ÷ 0.80
    x = 100
    Answer: 100
  9. A student scored 34 out of 40. What percentage is this?

    View hint and full working

    Hint: Divide the score by the total and multiply by 100.

    Working
    34 ÷ 40 = 0.85
    0.85 × 100% = 85%
    Answer: 85%
  10. A value increases from 40 to 50. What is the percentage increase?

    View hint and full working

    Hint: Divide the increase by the original value, not the new value.

    Working
    Increase = 50 − 40 = 10
    10 ÷ 40 = 0.25
    0.25 × 100% = 25%
    Answer: 25%

Level 3 Percentage Word Problems — Hard 10 questions · Advanced applications 0/10

Tip: Use decimal multipliers for reverse percentages and successive changes. Do not simply add successive percentage changes.
  1. After a 15% increase, the price is 230. Find the original price.

    View hint and full working

    Hint: The final price is 115% of the original price.

    Working
    Let the original price be x.
    1.15x = 230
    x = 230 ÷ 1.15
    x = 200
    Answer: 200
  2. A quantity is decreased by 30% and then increased by 20% to become 168. Find the original quantity.

    View hint and full working

    Hint: Multiply the two change factors before reversing the result.

    Working
    Decrease factor = 0.70
    Increase factor = 1.20
    Combined factor = 0.70 × 1.20 = 0.84
    0.84x = 168
    x = 168 ÷ 0.84
    x = 200
    Answer: 200
  3. A population is 5000 and grows by 8% per year for 2 years. Find the new population.

    View hint and full working

    Hint: Apply the growth factor 1.08 twice.

    Working
    5000 × 1.08²
    = 5000 × 1.1664
    = 5832
    Answer: 5832
  4. An item with a cost price of 160 is sold at a 15% loss. Find the selling price.

    View hint and full working

    Hint: A 15% loss means the selling price is 85% of the cost price.

    Working
    160 × (1 − 0.15)
    = 160 × 0.85
    = 136
    Answer: 136
  5. What percentage of 45 is 9?

    View hint and full working

    Hint: Divide 9 by 45 and multiply by 100.

    Working
    9 ÷ 45 = 0.2
    0.2 × 100% = 20%
    Answer: 20%
  6. 30% of x is 54. Find x.

    View hint and full working

    Hint: Write 30% as 0.30 and divide 54 by 0.30.

    Working
    0.30x = 54
    x = 54 ÷ 0.30
    x = 180
    Answer: 180
  7. A price rises from 150 to 180. What is the percentage increase?

    View hint and full working

    Hint: Divide the increase by the original price.

    Working
    Increase = 180 − 150 = 30
    30 ÷ 150 = 0.2
    0.2 × 100% = 20%
    Answer: 20%
  8. Two successive discounts of 10% and 20% are given. What is the net discount?

    View hint and full working

    Hint: Multiply the remaining-price factors 0.90 and 0.80.

    Working
    Remaining-price factor = 0.90 × 0.80
    = 0.72
    Net discount = 1 − 0.72
    = 0.28 = 28%
    Answer: 28%
  9. The final price is 110 including 10% GST. Find the price before GST.

    View hint and full working

    Hint: The GST-inclusive price is 110% of the original price.

    Working
    Let the original price be x.
    1.10x = 110
    x = 110 ÷ 1.10
    x = 100
    Answer: 100
  10. An amount becomes 918 after increasing by 2% each month for 6 months. Find the original amount. Round to the nearest cent.

    View hint and full working

    Hint: Reverse the compound increase by dividing by 1.02 raised to the sixth power.

    Working
    Let the original amount be x.
    x × 1.02⁶ = 918
    x = 918 ÷ 1.02⁶
    x ≈ 815.1577
    Rounded to the nearest cent: 815.16
    Answer: 815.16

🧠 What Is a Percentage?

“Percent” means “per hundred”. A percentage is a fraction with a denominator of 100.
Example: 75% means 75/100.

We have seen 50% off sign at your various stores or received an exam score of 80%. That’s a percentage — a simple way to compare parts out of 100!

Humans began using percentages because they make numbers easier to understand and compare. Instead of saying something confusing like “1349 out of 1589 students passed,” we can simply say “85% of students passed.” A percentage shows how much of something you have out of a total of 100 parts. It instantly gives a clear picture of the data, helping us grasp information quickly without doing complex calculations.

Thus, Percentages are another way to write fractions and decimals — all three mean the same thing, just in different forms. 

 

Conversions Formulae to Calculate Percentages Easily

The key formula to calculate percentages easily is to multiply the number/fraction/decimal by 100:

 

a) Fraction → Percentage

Multiply the fraction by 100. Example: (3/4) × 100 = 75%

b) Decimal → Percentage

Multiply the decimal by 100. Example: 0.65 × 100 = 65%

c) Percentage → Fraction

Write the percentage over 100, then simplify. Example: 40% = 40/100 = 2/5

d) Percentage → Decimal

Divide by 100. Example: 75% = 0.75

 

Finding a Percentage of a Number

Multiply the number by the percentage (in decimal form).

Example: 20% of 250 = 0.20 × 250 = 50

Reverse Percentage

Used when the percentage and result are given, but the original number is unknown.

Example: 20% of x = 36 → x = 36 ÷ 0.20 = 180

Percentage Increase / Decrease

Increase: New value = Original value × (1 + Increase%/100)

Decrease: New value = Original value × (1 – Decrease%/100)

Example: Increase 200 by 15%: 200 × 1.15 = 230

Percentage Change

Percentage change = (Difference / Original value) × 100

If the value goes up → increase.

If the value goes down → decrease.

 

💡 Real-Life Examples of Percentages

Percentages are everywhere — in shopping, school, sports, and even money matters. Learning to calculate percentages easily helps students make smarter decisions every day.

When shopping, discounts are given as percentages. For example, if a jacket costs $100 and there’s a 20% discount, you save $20, paying only $80. Knowing this helps you quickly spot the best deals.

In school, exam marks are also shown as percentages. If you get 45 out of 50 answers correct, that’s (45 ÷ 50) × 100 = 90% — a clear way to see your performance.

Sports use percentages too. A basketball player with a 75% free-throw rate scores about 75 out of every 100 shots, making it easy to compare skills.

Percentages also appear in money and savings. Banks pay interest as a percentage of your balance — the higher the percentage, the faster your money grows.

From sales to schoolwork, understanding how to calculate percentages easily helps you make sense of numbers in everyday life.

 

Common Percentage Mistakes Students Make

Even when students learn how to calculate percentages easily, small mistakes can still sneak in and change the answer completely.

A common error is dividing instead of multiplying. Remember — to find a percentage of a number, you multiply the number by the decimal form of the percentage. For example, 20% of 150 = 150 × 0.20 = 30.

Another mistake is forgetting to convert percentages into decimals before calculating. Just divide the percentage by 100 to make it a decimal:
👉 25% = 0.25 👉 10% = 0.10 👉 75% = 0.75

Students also mix up percentage increases and decreases. A 50% increase followed by a 50% decrease won’t return you to the original number, because each change is calculated from a different base value.

By slowing down and checking each step, students can avoid these errors and calculate percentages confidently and correctly every time.

 

⚡ Quick Tips and Tricks to Learn Percentages Faster

Learning percentages doesn’t have to be hard — with a few smart tricks, you can calculate percentages easily and save time in exams or real life.

A great shortcut is estimation. To find 25% of a number, just divide it by 4, since 25% equals one-quarter. For 50%, simply find half — no calculator needed!

Another trick is to remember common percentage conversions.
👉 10% of a number = divide by 10
👉 20% = double the 10% value
👉 30% = add 10% + 20%
Breaking percentages into smaller, easy chunks makes mental maths much faster.

You can also visualise percentages using pie charts or bar graphs. Seeing how a part fits into a whole helps you understand the concept better — especially for topics like discounts or statistics.

And of course, practice makes perfect. The more you solve percentage questions, the quicker and more confident you’ll become at spotting shortcuts and applying them correctly.

With these simple strategies, you’ll be able to calculate percentages easily, accurately, and confidently — anytime, anywhere!

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