GCSE Maths Practice: decimals

Subtracting Decimals

Subtracting decimals works just like subtracting whole numbers — the key is lining up the decimal points so each digit stays in the correct place value. Once aligned, you can subtract from right to left, borrowing when necessary, and keep the decimal point directly in line in your final answer.

Step-by-Step Method

1. Write the numbers vertically, making sure the decimal points are aligned.
2. Add zeros if needed so both numbers have the same number of digits after the decimal.
3. Start subtracting from the smallest place value (hundredths).
4. Borrow from the next place value if the top digit is smaller than the bottom digit.
5. Place the decimal point in the answer directly below the others.

Worked Examples

Example 1: 4.3 − 1.25 = ?
Write as 4.30 − 1.25 = 3.05.

Example 2: 7.82 − 3.5 = ?
Write as 7.82 − 3.50 = 4.32.

Example 3: 10.5 − 2.75 = ?
Write as 10.50 − 2.75 = 7.75.

Example 4: 6.04 − 0.38 = ?
Write as 6.04 − 0.38 = 5.66.

Common Mistakes

• Misaligned decimals: If you don’t align the decimal points, digits shift into the wrong place values, leading to errors.
• Forgetting placeholder zeros: When one number has fewer decimal digits, always add zeros to balance them before subtracting.
• Wrong direction when borrowing: Borrow only from the next left column and adjust digits carefully.

Real-Life Applications

Subtracting decimals is common in money, distance, and measurement problems. For example, if an item costs £5.60 and you pay £2.47, you receive £3.13 change. If a car travels 5.6 km and a cyclist travels 2.47 km, the difference is 3.13 km. These simple operations appear in budgeting, scientific calculations, and everyday reasoning.

FAQs

1. What’s the easiest way to check my subtraction?
Add the answer to the smaller number. If it gives the original number, your subtraction is correct.

2. Can I use mental maths for decimals?
Yes, for simple tenths or halves, but for more decimal places, it’s safer to write them vertically.

3. Why add zeros at the end of decimals?
To ensure the numbers have equal decimal places — it doesn’t change the value but prevents alignment errors.

4. What if the result ends in a zero?
For example, 5.4 − 2.9 = 2.5 — you don’t need to write 2.50 unless the context (like money) requires it.

Study Tip

Use grid paper or lined paper to keep decimals vertically aligned when subtracting. Practise with everyday money values — e.g. £6.25 − £2.47 or £4.50 − £1.35 — to build fluency for exams and life applications.

Subtracting decimals accurately builds confidence in number handling and forms the foundation for problem-solving with money, measurement, and percentages in GCSE Maths.