GCSE Maths Practice: decimals

Question 1 of 10

This GCSE Maths foundation question helps you practise converting decimals into percentages. It strengthens your understanding of place value, proportion, and how percentages link decimals and fractions together.

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\( \begin{array}{l}\textbf{Write } 0.25 \textbf{ as a percentage.}\end{array} \)

Choose one option:

Always multiply decimals by 100 to turn them into percentages. The decimal point moves two places to the right, and you add the % symbol.

Understanding the Decimal–Percentage Link

Decimals, fractions, and percentages are three connected ways of expressing the same quantity. Decimals use powers of ten, fractions use parts of a whole, and percentages use parts per hundred. Converting between them is an essential GCSE skill that helps you move quickly between topics such as ratio, interest, and probability.

To convert a decimal into a percentage, multiply by 100 because 'percent' means 'per hundred.' Each place you move the decimal point to the right multiplies the value by ten. Two places to the right multiplies it by one hundred.

Step-by-Step Method

  1. Write down the decimal.
  2. Multiply the number by 100.
  3. Attach the percentage sign (%).

For example:

  • 0.25 → 25%
  • 0.5 → 50%
  • 0.75 → 75%
  • 1.0 → 100%

Each value shows how the decimal grows as you move the decimal point two places to the right.

Worked Examples

Example 1: Convert 0.6 to a percentage.
0.6 × 100 = 60 → 60%.

Example 2: Convert 0.04 to a percentage.
0.04 × 100 = 4 → 4%.

Example 3: Convert 0.125 to a percentage.
0.125 × 100 = 12.5 → 12.5%.

Example 4: Convert 1.2 to a percentage.
1.2 × 100 = 120 → 120% (more than a whole).

Common Mistakes

  • Moving the decimal the wrong way: Always move it two places to the right when multiplying by 100, not to the left.
  • Forgetting the % symbol: Without it, the answer is still a decimal, not a percentage.
  • Confusing decimals smaller than 1: 0.04 is 4%, not 40% — double-check the place value.

Real-Life Applications

Percentages are everywhere — in sales discounts, exam results, and data analysis. For example, if £40 is reduced by 25%, you can recognise that 25% = 0.25, meaning one quarter off the price. A student who scores 0.75 on a test achieves 75%. Converting between these forms helps with budgeting, problem-solving, and interpreting statistics.

FAQs

1. How do I convert a percentage back to a decimal?
Divide by 100. For example, 25% ÷ 100 = 0.25.

2. What does 100% mean?
It means a complete whole — the same as 1 in decimal form.

3. Can percentages be more than 100%?
Yes, if something increases beyond its original value, like a 120% rise in sales.

4. Why multiply by 100?
Because 'percent' literally means 'per hundred,' and multiplying scales the number to that base.

Study Tip

Memorise the key equivalents: 0.25 = 25%, 0.5 = 50%, 0.75 = 75%, and 1 = 100%. These are benchmark conversions that appear frequently in GCSE questions. Writing a mini-table of these helps improve accuracy and speed.

Understanding how decimals link to percentages makes many GCSE topics easier — from financial calculations to data interpretation and proportion problems.