GCSE Maths Practice: decimals

Question 4 of 10

This question checks your ability to add decimals accurately by aligning the decimal points. It helps you practise correct place value, a vital skill in GCSE Maths when working with money, measurements, and data.

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\( \begin{array}{l}\textbf{Calculate } 2.7 + 1.45.\end{array} \)

Choose one option:

Always align the decimal points when adding or subtracting decimals. Add zeros if necessary so each number has the same number of digits after the decimal point.

Adding and Subtracting Decimals

Adding and subtracting decimals follows the same principles as adding whole numbers — the only difference is that you must line up the decimal points carefully. This ensures that tenths, hundredths, and thousandths line up under each other, maintaining correct place value.

Step-by-Step Method

  1. Write the numbers one under the other, aligning the decimal points.
  2. Add placeholder zeros if one number has fewer decimal places.
  3. Start adding or subtracting from the rightmost digits (the smallest place value).
  4. Carry or borrow as needed, just like in whole number addition or subtraction.
  5. Place the decimal point in your answer directly below the others.

Worked Examples

Example 1: 3.6 + 1.45 = ?
3.60 + 1.45 = 5.05.

Example 2: 5.4 − 2.75 = ?
5.40 − 2.75 = 2.65.

Example 3: 12.35 + 0.7 = ?
12.35 + 0.70 = 13.05.

Example 4: 9.5 − 4.28 = ?
9.50 − 4.28 = 5.22.

Notice how zeros were added so that each number has the same number of decimal places — this keeps each column aligned.

Common Mistakes

  • Forgetting to align decimals: Misalignment can lead to incorrect results (e.g. treating 2.7 + 1.45 as 27 + 1.45).
  • Omitting placeholder zeros: Always make sure both numbers have equal decimal digits before adding or subtracting.
  • Placing the decimal point incorrectly: The decimal in the answer should line up vertically with the others.

Real-Life Applications

This skill is vital for working with money, measurements, and data. For example, when combining £2.70 and £1.45, the total is £4.15. Similarly, adding 2.7 kg of apples and 1.45 kg of oranges gives 4.15 kg in total. Understanding decimal addition ensures accuracy in financial calculations, recipes, science experiments, and everyday estimations.

FAQs

1. Can I add decimals without lining them up?
No. Without alignment, you mix up place values and get incorrect results.

2. What if the decimals have different lengths?
Add zeros so that they have the same number of decimal places.

3. How can I check my answer?
Estimate roughly first — 2.7 + 1.45 ≈ 2.7 + 1.5 = 4.2 — to see if your final answer makes sense.

4. Do subtraction and addition follow the same rule?
Yes — always line up decimals in both cases.

Study Tip

Practise by writing simple money problems: £3.45 + £2.7, £4.20 − £1.75, £0.65 + £1.4. Visualise the decimal point like a boundary that never moves. Every digit must stay in its correct place value column.

Being confident at adding and subtracting decimals strengthens problem-solving in money, measurement, and data questions throughout GCSE Maths.