Adding & Subtracting Decimals

Name:

Date:

🔢 Part 1: Basic Decimal Operations

1. First, estimate each answer by rounding to the nearest whole number. Then calculate the exact answer.

a) 3.45 + 2.78

Estimate: _____ + _____ = _____

Exact answer: __________

b) 7.62 - 4.19

Estimate: _____ - _____ = _____

Exact answer: __________

2. Calculate these three decimal place problems. Show your working by aligning decimal points correctly.

a) 12.456 + 8.739 = __________

b) 15.834 - 7.567 = __________

💰 Part 2: Real-World Problems

3. Sarah is shopping for school supplies. She buys a notebook for $4.75, pens for $3.25, and a ruler for $2.45. How much does she spend in total?

Answer: $__________

4. A recipe calls for 2.375 litres of water. Jake has already added 1.850 litres. How much more water does he need to add?

Answer: __________ litres

5. The temperature in Auckland was 18.7°C at midday. By evening, it had dropped by 5.8°C. What was the evening temperature?

Answer: __________°C

6. Emma ran 3.45 kilometres on Monday and 2.78 kilometres on Tuesday. On Wednesday, she ran 4.12 kilometres. What was her total distance for the three days?

Answer: __________ kilometres

🧠 Part 3: Problem Solving & Reasoning

7. Tom has $20.00 to spend at the school canteen. He buys lunch for $7.85 and a drink for $2.35. How much money does he have left?

First estimate your answer: $__________

Exact answer: $__________

8. A carpenter needs to cut a piece of wood that is 3.750 metres long into two pieces. If one piece is 1.425 metres long, what is the length of the other piece?

Answer: __________ metres

9. Explain in your own words why it's important to line up decimal points when adding or subtracting decimals.

10. Check this student's work. Is it correct? If not, explain the mistake and show the correct calculation.

Student's work:

4.56 + 12.3 = 16.86