➕ Decimal Dash: Add & Subtract Decimals 💨

Adding and subtracting decimals works exactly like whole numbers — the KEY rule is to ALWAYS line up the decimal points before you calculate! In Grade 6, you'll work with decimals up to 3 decimal places in real contexts like money, measurement and science.

📍 Line Up the Points!
   3.47
+ 1.80
= 5.27 — write 1.8 as 1.80 to keep decimal points aligned
🔄 Estimate First
12.73 − 4.85 ≈ 13 − 5 = 8
Exact: 7.88. Estimate confirms the answer!
💰 Real-Life Decimals
£8.57 + £3.46 = £12.03
money is always 2 decimal places!

⭐ The Golden Rules

  • ALWAYS line up the decimal points when writing numbers in columns. The decimal point stays in the same vertical position in the answer.
  • Fill gaps with zeros to make alignment clearer. E.g., 4.3 + 1.75 → write 4.30 + 1.75.
  • Add and subtract digit by digit from right to left (same as whole numbers). Carry and borrow work the same way.
  • Always estimate first by rounding to the nearest whole number. Your estimate should be close to your answer.
  • Check using inverse: if you calculated a + b = c, then c − b should give a.
  • In money calculations, always give answers to 2 d.p. (e.g., £5.30, not £5.3).
  • In measurement, keep consistent units before adding (convert if needed).
3.47 + 1.80 = 5.27

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

📖 Worked Examples

Example 1: Decimal Addition (column method)

Calculate 5.47 + 3.826

Step 1: Write with decimal points aligned — fill the gap with 0: 5.470 + 3.826
Step 2: Thousandths: 0 + 6 = 6
Step 3: Hundredths: 7 + 2 = 9
Step 4: Tenths: 4 + 8 = 12 → write 2, carry 1
Step 5: Ones: 5 + 3 + 1 (carried) = 9
5.470
+ 3.826
9.296
✅ Estimate check: 5 + 4 = 9 ✓   Answer: 9.296

Example 2: Decimal Subtraction (column method)

Calculate 8.3 − 2.746

Step 1: Write with decimal points aligned — fill gaps with zeros: 8.300 − 2.746
Step 2: Thousandths: 0 − 6 → borrow: 10 − 6 = 4
Step 3: Hundredths: (3−1) − 4 → borrow: 12 − 4 = 5 (after borrowing from tenths)
Step 4: Continue performing column subtraction with borrowing where needed
8.300
− 2.746
5.554
✅ Check: 5.554 + 2.746 = 8.300 ✓   Answer: 5.554

Example 3: Money — Multi-step

Emma buys a book for £7.45 and a pen for £1.99. She pays with a £10 note. How much change does she receive?

Step 1: Find total cost: £7.45 + £1.99
£7.45
+ £1.99
£9.44
Step 2: Find change: £10.00 − £9.44
£10.00
− £9.44
£0.56
✅ Answer: Emma receives 56p change.

Example 4: Measurement — Perimeter

A rectangle has length 4.35m and width 2.8m. Find the perimeter.

Step 1: Write 2.8m as 2.80m to align decimal places
Step 2: Add length + width: 4.35 + 2.80 = 7.15m
4.35
+ 2.80
7.15
Step 3: Perimeter = 2 × 7.15 = 14.30m
✅ Answer: Perimeter = 14.3m

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🔬 Decimal Column Solver

Enter two decimals and an operation to see step-by-step working.

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 1: Decimal Addition

Calculate 3.7 + 2.45

Drag the correct answer into the drop zone!

6.15
6.25
5.15
6.12
3.7 + 2.45 =
?

💡 Hint: Write 3.70 + 2.45. Line up the points!

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 2: Decimal Subtraction

Calculate 9.3 − 4.78

Drag the correct answer into the drop zone!

4.42
4.52
5.52
4.48
9.3 − 4.78 =
?

💡 Hint: Write 9.30 − 4.78. Borrow carefully!

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 3: Money Addition

A sandwich costs £3.65 and a drink costs £1.48. What is the total?

Drag the correct answer into the drop zone!

£4.13
£5.13
£5.03
£4.93
£3.65 + £1.48 =
?

💡 Hint: £3.65 + £1.48. 5+8=13, write 3, carry 1...

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 4: Money Change

You pay £10 for items costing £6.47. What change do you receive?

Drag the correct answer into the drop zone!

£3.53
£3.63
£4.53
£3.43
£10.00 − £6.47 =
?

💡 Hint: £10.00 − £6.47. Borrow from the whole number.

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 5: Three Decimal Addition

Calculate 1.234 + 2.567 + 0.8

Drag the correct answer into the drop zone!

4.501
4.601
4.511
4.401
1.234 + 2.567 + 0.8 =
?

💡 Hint: Write 1.234 + 2.567 + 0.800. Add column by column.

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🎯 Drag 6: Measurement Subtraction

A piece of wood is 3.5m long. A 1.375m section is cut off. How much is left?

Drag the correct answer into the drop zone!

2.125m
2.025m
1.825m
2.225m
3.5 − 1.375 =
?

💡 Hint: 3.500 − 1.375. Line up the decimal points!

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

✏️ Practice Questions

Work through these 20 questions. Remember to line up the decimal points!

  1. 4.3 + 2.5 = ?
  2. 7.8 − 3.4 = ?
  3. 5.47 + 3.26 = ?
  4. 9.65 − 4.38 = ?
  5. 12.5 + 6.75 = ?
  6. 20.0 − 7.43 = ?
  7. 3.456 + 2.374 = ?
  8. 8.002 − 3.67 = ?
  9. 0.75 + 0.485 = ?
  10. 5.0 − 2.375 = ?
  11. £4.56 + £7.89 = ?
  12. £20.00 − £13.67 = ?
  13. 6.3 + 1.45 + 2.7 = ?
  14. 14.7 − 8.625 = ?
  15. A jug holds 2.5 litres. 0.875 litres is poured out. How much remains?
  16. 0.037 + 0.246 = ?
  17. 100.0 − 43.75 = ?
  18. 3.7 + 4.83 + 1.006 = ?
  19. A runner's time improves from 14.73 seconds to 13.56 seconds. By how much?
  20. 7 − 2.846 = ?

✅ Answers

  1. 4.3 + 2.5 = 6.8
  2. 7.8 − 3.4 = 4.4
  3. 5.47 + 3.26 = 8.73
  4. 9.65 − 4.38 = 5.27
  5. 12.5 + 6.75 = 19.25
  6. 20.0 − 7.43 = 12.57
  7. 3.456 + 2.374 = 5.830
  8. 8.002 − 3.67 = 4.332
  9. 0.75 + 0.485 = 1.235
  10. 5.0 − 2.375 = 2.625
  11. £4.56 + £7.89 = £12.45
  12. £20.00 − £13.67 = £6.33
  13. 6.3 + 1.45 + 2.7 = 10.45
  14. 14.7 − 8.625 = 6.075
  15. A jug holds 2.5 litres. 0.875 litres is poured out. How much remains? → 1.625 litres
  16. 0.037 + 0.246 = 0.283
  17. 100.0 − 43.75 = 56.25
  18. 3.7 + 4.83 + 1.006 = 9.536
  19. A runner's time improves from 14.73 seconds to 13.56 seconds. By how much? → 1.17 seconds
  20. 7 − 2.846 = 4.154

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush

🏆 Challenge Problems

These problems require multiple steps and real-world thinking. Show all your working!

  1. Sam buys three items: £2.49, £5.75 and £3.08. He has £12. Does he have enough? How much is left (or how much more does he need)?
  2. A swimming pool loses 0.375m of water per day by evaporation. It starts at 1.9m deep. What is the depth after 3 days?
  3. Four lengths of ribbon measure 3.45m, 2.8m, 1.75m and 4.025m. What is the total length?
  4. A number plus 4.783 equals 10. What is the number?
  5. Petrol costs £1.487 per litre at one garage and £1.532 per litre at another. How much more does 10 litres cost at the dearer garage?
  6. Tom runs three laps in 1.246 minutes, 1.305 minutes and 1.19 minutes. What is his total time?
  7. A farmer's field is 8.75m wide. After extending by 2.375m, then removing a 0.8m strip for a path, what is the new total width?
  8. In a science experiment, liquid A weighs 4.567g and liquid B weighs 3.89g. Together they weigh less than 9g. By how much?
  9. A temperature drops from 12.4°C to −3.8°C overnight. How much did it fall?
  10. The three sides of a triangle measure 5.45cm, 4.8cm and 6.375cm. Find the perimeter.

✅ Challenge Answers

  1. Total = £2.49 + £5.75 + £3.08 = £11.32
    £12.00 − £11.32 = £0.68 left. Yes, Sam has enough money.
  2. Water lost in 3 days = 0.375 × 3 = 1.125m
    Depth after 3 days = 1.9 − 1.125 = 0.775m
  3. 3.45 + 2.80 + 1.75 + 4.025 = 12.025m
  4. ? + 4.783 = 10 → 10 − 4.783 = 5.217
  5. Difference per litre = £1.532 − £1.487 = £0.045
    10 × £0.045 = £0.45 more at the dearer garage
  6. 1.246 + 1.305 + 1.190 = 3.741 minutes
  7. 8.75 + 2.375 − 0.8 = 10.325m
  8. A + B = 4.567 + 3.89 = 8.457g
    9 − 8.457 = 0.543g less than 9g
  9. Fall = 12.4 + 3.8 = 16.2°C (since −3.8°C is below 0)
  10. 5.45 + 4.80 + 6.375 = 16.625cm

Unit 14 · Collins Stage 6 Cambridge Primary Maths · FractionRush