Maths Facts
Why estimates are useful
Explain how guesses help check answers and plan methods.
Quick answer
Estimates help us check if our answers are sensible and help us plan how to solve problems more easily.Learning outcome
By the end of this page, you will understand why estimating numbers is useful and how to use estimates to check your maths. Success signs:- You can make a quick guess about how many items are in a group
- You can use estimates to check if your answer is reasonable
- You can use estimates to plan your method before solving a problem
- You can explain why estimating helps in everyday life
Why this matters
Estimating is like being a detective with maths. When you estimate, you're making a smart guess to check if your answer is close to the right amount. This helps you catch silly mistakes, plan your work, and make better decisions. Whether you're sharing sweets, planning a party, or shopping for groceries, estimates help you think quickly and make smart choices.How it works
Estimating means making a good guess about a number without doing exact calculations. You can estimate by:- Rounding numbers to the nearest 10 or 100
- Using known facts to make a reasonable guess
- Looking at the size of numbers to decide if your answer is likely to be big or small
Examples you can see
Let’s try some examples to show how estimates work in real life. Example 1: Sharing sweets Imagine you have 42 sweets and want to share them equally among 5 friends. You can estimate how many each friend might get by rounding 42 to 40. Then, 40 ÷ 5 = 8. So each friend gets about 8 sweets. This helps you plan your sharing without needing to work out the exact answer first. Example 2: Shopping You want to buy a toy that costs £19.99 and a book that costs £8.50. You can estimate the total by rounding £19.99 to £20 and £8.50 to £9. So your estimate is £20 + £9 = £29. If your final total is £28.49, your estimate was close, so you know you've got the right amount. Example 3: Measuring a room You want to buy carpet for a room that's about 6.3 metres long and 4.7 metres wide. You can estimate the area by rounding to 6 metres and 5 metres. So your estimate is 6 × 5 = 30 square metres. If you later calculate the exact area and it's 30.8 square metres, your estimate was very close.Try it as a mini adventure
Adventure: The Estimator's Quest You are on a quest to help a shopkeeper plan how many bags of apples to order. The shopkeeper needs to know how many apples to expect in a week.- First day: 32 apples
- Second day: 41 apples
- Third day: 29 apples
- Fourth day: 37 apples
- Fifth day: 34 apples
- Round each day's apple count to the nearest 10:
- 32 → 30
- 41 → 40
- 29 → 30
- 37 → 40
- 34 → 30
Common mistakes
- Mistake: Not rounding numbers to make estimates easier.
Why it happens: Children may think they must calculate exactly, not make a smart guess.
Fix: Practice rounding to the nearest 10 or 100 to make estimating easier. - Mistake: Thinking estimates are only for rough answers.
Why it happens: Children might not understand that estimates help check answers.
Fix: Use estimates to double-check your final answers. - Mistake: Using estimates to avoid working hard.
Why it happens: Some children may think estimates are just "not doing the work."
Fix: Explain that estimates help you do work smarter, not less.
Parent and carer guide
As a parent or carer, you can help your child understand estimates by:- Practising rounding numbers to the nearest 10 or 100 in everyday situations
- Asking questions like "About how many?" when shopping or cooking
- Encouraging your child to check their answers with a quick estimate
- Using real-life examples like planning a party or filling a container
- Not worrying if the estimate is not exactly right – the idea is to be close
- "Let’s guess how many crayons are in this box."
- "What do you think the answer will be before you calculate?"
- "Is your answer close to your estimate?"
- Whether the estimate is perfect – it's about being close
- Whether your child is fast at estimating – it's about thinking smartly
Practice questions
- Estimate the sum of 28 + 37.
- Estimate the product of 6 × 8.
- If a box has 47 marbles and you want to share them among 7 friends, about how many will each friend get?
- Estimate the total cost of a £12.99 book and a £7.50 toy.
- If a football team scores 23, 18, 27, and 21 points in four games, about how many points did they score in total?
- 28 → 30, 37 → 40. Estimate: 30 + 40 = 70
- 6 × 8 = 48. Estimate: 6 × 8 = 48 (no rounding needed)
- 47 → 50. 50 ÷ 7 ≈ 7. So about 7 marbles each
- £12.99 → £13, £7.50 → £8. Estimate: £13 + £8 = £21
- 23 → 20, 18 → 20, 27 → 30, 21 → 20. Estimate: 20 + 20 + 30 + 20 = 90
FAQ
Why do we need to estimate?
Estimates help us check if our answers make sense and help us plan how to solve problems. They save time and help us avoid silly mistakes.
Can I use estimates for subtraction?
Yes! You can round numbers before subtracting to get a quick estimate. For example, 53 - 28 can be estimated as 50 - 30 = 20.
How do I know if my estimate is good?
If your estimate is close to your actual answer, it’s a good estimate. The closer it is, the better.
Do I have to use estimates in maths tests?
Not always, but using estimates helps you check your work and makes you more confident in your answers.
Can I estimate with decimals?
Yes! You can round decimals to the nearest whole number or tenth to estimate. For example, 3.7 + 2.8 can be estimated as 4 + 3 = 7.