📚 Detailed Explanation of Estimating Sums
When you are working on addition problems in Year 3, learning how to estimate sums can really help you check your answers quickly and understand numbers better. Estimating means finding a number that is close to the exact answer but easier to calculate in your head.
🤔 What Does Estimating Sums Mean?
Estimating sums means adding numbers together in a way that gives an answer that is close to the real total but is quicker to work out. This is useful when the exact calculation is hard or when you want to check if your exact answer makes sense.
🔢 How to Estimate Sums by Rounding
One of the easiest methods to estimate sums is by rounding numbers before adding them. When we round numbers, we change them to the nearest ten or hundred.
- Rounding to the nearest ten: Look at the number’s ones digit (the last number).
- If it’s 5 or more, round the number up to the next ten.
- If it’s less than 5, round the number down to the previous ten.
- Rounding to the nearest hundred: Look at the number’s tens digit.
- If it’s 5 or more, round the number up to the next hundred.
- If it’s less than 5, round down to the previous hundred.
✏️ Examples of Estimating Sums
- Example using rounding to the nearest ten:
Add 47 + 36.- Round 47 to 50 (because 7 is more than 5).
- Round 36 to 40 (because 6 is more than 5).
- Add your rounded numbers: 50 + 40 = 90.
So, the estimated sum is about 90. The exact sum is 83, so the estimate helps you see the total is close to 90.
- Example using rounding to the nearest hundred:
Add 235 + 478.- Round 235 to 200 (because 3 is less than 5).
- Round 478 to 500 (because 7 is more than 5).
- Add your rounded numbers: 200 + 500 = 700.
The estimated sum is about 700. The exact sum is 713, so this is a good quick estimate.
👍 Why Estimating Sums is Helpful
- It helps you check if your answer is reasonable.
- It is faster for mental maths when you don’t need the exact total.
- It improves your understanding of place value and number sizes.
💡 Tips for Estimating Sums
- Always decide if rounding to the nearest ten or hundred makes more sense for the numbers you have.
- Practice rounding different numbers so you feel confident estimating.
- Use estimation to check your work after adding numbers exactly.
Keep practising estimating sums, and it will soon become easier and quicker for you to use in your maths work! 🎉
📝 20 Examination-Style Questions on Estimating Sums for Year 3
Here are 20 examination-style questions focused on estimating sums, suitable for Year 3 students following the UK National Curriculum. These questions include multiple-choice, fill-in-the-blanks, and word problems, with varying difficulty to help practice estimating sums.
❓ Multiple Choice Questions
- Estimate the sum of 27 + 35 by rounding each number to the nearest ten. What is the estimated sum?
- a) 50
- b) 60
- c) 70
- d) 80
- What is the estimated sum of 64 + 18? (Round each number to the nearest ten first.)
- a) 70
- b) 80
- c) 90
- d) 100
- Estimate 48 + 53 by rounding each number to the nearest ten. What is the answer?
- a) 80
- b) 90
- c) 100
- d) 110
- Which estimated sum is closest to 93 + 27?
- a) 110
- b) 120
- c) 130
- d) 140
- Estimate the sum of 15 + 29.
- a) 30
- b) 40
- c) 50
- d) 60
✍️ Fill in the Blanks
- Round 38 to the nearest ten: ____
Round 44 to the nearest ten: ____
Estimated sum of 38 + 44 is ____. - Estimated sum of 57 + 22 (rounded to nearest ten) is ____.
- Round 15 and 65 to the nearest ten. The estimated sum is ____.
- What is the estimated sum of 76 + 84 when rounded to the nearest ten? ____
- Estimate the sum of 33 + 47 by rounding both numbers to the nearest ten. The answer is ____.
🧩 Word Problems
- Liam has 29 marbles and Lily has 65 marbles. Estimate how many marbles they have together by rounding to the nearest ten.
- Sarah bought two books. One cost £47 and the other cost £36. Estimate the total cost by rounding each price to the nearest ten.
- There are 58 apples and 67 oranges in the basket. Estimate the total number of fruits by rounding to the nearest ten.
- A train travels 83 miles in the morning and 27 miles in the afternoon. Estimate the total distance travelled.
- Tom reads 34 pages on Monday and 46 pages on Tuesday. Estimate the total number of pages read.
🔀 Mixed Question Types
- Multiple Choice: Estimate 72 + 19 by rounding each number to the nearest ten. What is the estimated sum?
- a) 80
- b) 90
- c) 100
- d) 110
- Fill in the blank: The estimated sum of 49 + 38 is ____.
- Word Problem: Anna collects 34 stickers and Ben collects 56 stickers. Estimate the total stickers they collected by rounding to the nearest ten.
- Multiple Choice: Estimate the sum of 23 + 75.
- a) 80
- b) 90
- c) 100
- d) 110
- Fill in the blank: Round 67 and 24 to the nearest ten. Their estimated sum is ____.
These questions will help Year 3 students practise estimating sums by rounding numbers and making quick calculations, which is an important skill in mental maths and everyday problem-solving. 🚀
✅ Answers to the 20 Examination-Style Questions on Estimating Sums
Here are the complete answers and worked solutions to 20 Year 3 Key Stage 2 examination-style questions on estimating sums. Each solution shows the clear method used to estimate sums by rounding, which is an important skill in estimating sums quickly and checking answers.
1. Estimate the sum of 27 + 35.
Step 1: Round 27 to the nearest ten → 30
Step 2: Round 35 to the nearest ten → 40
Step 3: Add the rounded numbers → 30 + 40 = 70
Estimated sum: 70
2. Estimate the sum of 48 + 16.
Step 1: Round 48 to the nearest ten → 50
Step 2: Round 16 to the nearest ten → 20
Step 3: Add the rounded numbers → 50 + 20 = 70
Estimated sum: 70
3. Estimate the sum of 62 + 19.
Step 1: Round 62 to the nearest ten → 60
Step 2: Round 19 to the nearest ten → 20
Step 3: Add the rounded numbers → 60 + 20 = 80
Estimated sum: 80
4. Estimate the sum of 53 + 44.
Step 1: Round 53 to the nearest ten → 50
Step 2: Round 44 to the nearest ten → 40
Step 3: Add the rounded numbers → 50 + 40 = 90
Estimated sum: 90
5. Estimate the sum of 84 + 27.
Step 1: Round 84 to the nearest ten → 80
Step 2: Round 27 to the nearest ten → 30
Step 3: Add the rounded numbers → 80 + 30 = 110
Estimated sum: 110
6. Estimate the sum of 71 + 88.
Step 1: Round 71 to the nearest ten → 70
Step 2: Round 88 to the nearest ten → 90
Step 3: Add the rounded numbers → 70 + 90 = 160
Estimated sum: 160
7. Estimate the sum of 39 + 42 + 18.
Step 1: Round 39 → 40
Step 2: Round 42 → 40
Step 3: Round 18 → 20
Step 4: Add the rounded numbers → 40 + 40 + 20 = 100
Estimated sum: 100
8. Estimate the sum of 25 + 31 + 47.
Step 1: Round 25 → 30
Step 2: Round 31 → 30
Step 3: Round 47 → 50
Step 4: Add the rounded numbers → 30 + 30 + 50 = 110
Estimated sum: 110
9. Estimate the sum of 14 + 28 + 34.
Step 1: Round 14 → 10
Step 2: Round 28 → 30
Step 3: Round 34 → 30
Step 4: Add the rounded numbers → 10 + 30 + 30 = 70
Estimated sum: 70
10. Estimate the sum of 58 + 67 + 19.
Step 1: Round 58 → 60
Step 2: Round 67 → 70
Step 3: Round 19 → 20
Step 4: Add the rounded numbers → 60 + 70 + 20 = 150
Estimated sum: 150
11. Estimate the sum of 91 + 24 + 33.
Step 1: Round 91 → 90
Step 2: Round 24 → 20
Step 3: Round 33 → 30
Step 4: Add the rounded numbers → 90 + 20 + 30 = 140
Estimated sum: 140
12. Estimate the sum of 45 + 56 + 39.
Step 1: Round 45 → 50
Step 2: Round 56 → 60
Step 3: Round 39 → 40
Step 4: Add the rounded numbers → 50 + 60 + 40 = 150
Estimated sum: 150
13. Estimate the sum of 17 + 62 + 27.
Step 1: Round 17 → 20
Step 2: Round 62 → 60
Step 3: Round 27 → 30
Step 4: Add the rounded numbers → 20 + 60 + 30 = 110
Estimated sum: 110
14. Estimate the sum of 68 + 29 + 56.
Step 1: Round 68 → 70
Step 2: Round 29 → 30
Step 3: Round 56 → 60
Step 4: Add the rounded numbers → 70 + 30 + 60 = 160
Estimated sum: 160
15. Estimate the sum of 23 + 38 + 18.
Step 1: Round 23 → 20
Step 2: Round 38 → 40
Step 3: Round 18 → 20
Step 4: Add the rounded numbers → 20 + 40 + 20 = 80
Estimated sum: 80
16. Estimate the sum of 55 + 61 + 47.
Step 1: Round 55 → 60
Step 2: Round 61 → 60
Step 3: Round 47 → 50
Step 4: Add the rounded numbers → 60 + 60 + 50 = 170
Estimated sum: 170
17. Estimate the sum of 40 + 33 + 52.
Step 1: Round 40 → 40
Step 2: Round 33 → 30
Step 3: Round 52 → 50
Step 4: Add the rounded numbers → 40 + 30 + 50 = 120
Estimated sum: 120
18. Estimate the sum of 26 + 18 + 42.
Step 1: Round 26 → 30
Step 2: Round 18 → 20
Step 3: Round 42 → 40
Step 4: Add the rounded numbers → 30 + 20 + 40 = 90
Estimated sum: 90
19. Estimate the sum of 59 + 39 + 28.
Step 1: Round 59 → 60
Step 2: Round 39 → 40
Step 3: Round 28 → 30
Step 4: Add the rounded numbers → 60 + 40 + 30 = 130
Estimated sum: 130
20. Estimate the sum of 77 + 13 + 64.
Step 1: Round 77 → 80
Step 2: Round 13 → 10
Step 3: Round 64 → 60
Step 4: Add the rounded numbers → 80 + 10 + 60 = 150
Estimated sum: 150
🎯 Study Tip:
To estimate sums by rounding, always remember to round each number to the nearest ten before adding. This makes adding easier and faster. Estimation helps check if your exact answer makes sense. Keep practising rounding and adding to improve your confidence in estimating sums! 👍
