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Problem Solving

Estimation before calculation

Predict a sensible answer before solving exactly.

Quick answer

Estimation before calculation means guessing a sensible answer before doing the exact maths. It helps you check if your final answer makes sense.

Learning outcome

By the end of this page, you will be able to guess a reasonable answer before doing exact maths, so you can check if your final answer is right. Success signs:
  • You can make a good guess about how many items there are
  • You can decide if your final answer is close to your guess
  • You can use estimation to check if your maths is sensible
  • You can explain why your guess was reasonable

Why this matters

Estimation before calculation is a smart way to solve problems. It helps you:
  • Check if your answer is realistic
  • Save time by avoiding mistakes
  • Build confidence in maths
  • Use maths in real life, like shopping or cooking
Whether you are sharing cookies, planning a football game, or counting your toys, estimation helps you think before you calculate.

How it works

Estimation before calculation is simple:
  1. Look at the problem – What are you trying to find?
  2. Make a guess – What do you think the answer might be?
  3. Calculate exactly – Do the maths to find the real answer
  4. Check your guess – Is your real answer close to your guess?
This process helps you think carefully and avoid silly mistakes.

Examples you can see

Let's look at some examples you can imagine or draw. Example 1: Sharing sweets You have 24 sweets and 4 friends.
  • Guess: About 5 or 6 sweets each
  • Exact: 24 ÷ 4 = 6 sweets each
  • Check: Your guess was close!
Example 2: How many steps to school? You walk to school and take 200 steps.
  • Guess: About 200 steps
  • Exact: You count and find 200 steps
  • Check: Your guess was right!
Example 3: How many books on a shelf? You see a shelf with 3 rows of books, and each row has about 8 books.
  • Guess: About 24 books
  • Exact: 3 × 8 = 24 books
  • Check: Your guess was spot on!

Try it as a mini adventure

Adventure: The Great Toy Hunt You are on a mission to find toys in your house. You have 5 rooms to search.
  1. First room: You guess there are about 10 toys
  2. Second room: You guess there are about 15 toys
  3. Third room: You guess there are about 5 toys
  4. Fourth room: You guess there are about 20 toys
  5. Fifth room: You guess there are about 8 toys
Now, count the toys in each room exactly and write down the real number. Then, check how close your guesses were. Did you guess well? Challenge: Add up your guesses and your real counts. Which was higher?

Common mistakes

  • Mistake: Guessing too low or too high
    • Why it happens: Not thinking carefully about the numbers
    • Fix: Think about what the numbers mean. For example, if you are adding 23 + 18, think: "20 + 20 is about 40, so my answer should be near 40."
  • Mistake: Forgetting to check your guess
    • Why it happens: Rushing through the problem
    • Fix: Always take a moment to compare your guess to your final answer
  • Mistake: Guessing the wrong way
    • Why it happens: Not understanding what the question is asking
    • Fix: Read the question again and ask, "What am I trying to find?"

Parent and carer guide

Parents and carers can help by:
  • Asking questions like: "What do you think the answer might be?" before solving
  • Encouraging children to explain their guesses
  • Practising estimation in daily life, like shopping or cooking
  • Not worrying if the guess is not perfect – it's about thinking, not being right
  • Using real-life examples to show how estimation helps
How to help in 5 minutes:
  1. Ask your child to guess how many steps it is to the garden
  2. Then walk together and count
  3. Compare the guess to the real answer
  4. Ask: "Was your guess close?"
  5. Repeat with other simple things like toys or books
This helps build a habit of thinking before calculating.

Practice questions

  1. Estimate the answer to 12 + 17. Then calculate exactly.
  2. Estimate the answer to 25 ÷ 5. Then calculate exactly.
  3. Estimate the answer to 6 × 8. Then calculate exactly.
  4. Estimate the answer to 40 - 19. Then calculate exactly.
  5. Estimate the answer to 3 × 12. Then calculate exactly.
Answers:
  1. Guess: 30. Exact: 29
  2. Guess: 5. Exact: 5
  3. Guess: 50. Exact: 48
  4. Guess: 20. Exact: 21
  5. Guess: 36. Exact: 36

FAQ

What is estimation?

Estimation is guessing a reasonable answer before doing the exact maths. It helps you check if your answer makes sense.

Why do we estimate before calculating?

Estimating helps you think carefully about the problem. It helps you avoid silly mistakes and makes you more confident in your maths.

Can estimation be wrong?

Yes, estimation is just a guess. It doesn’t have to be perfect. The goal is to make a sensible guess that helps you check your work.

How can I practice estimation at home?

You can estimate while shopping, cooking, or counting things. Ask: "About how many?" before counting or calculating.

Is estimation only for maths?

No, estimation helps in many areas of life, like planning time, guessing how long a task will take, or sharing food.