---
title: "Estimation to check answers to calculations"
description: "Use estimation to check answers to calculations and determine, in the context of a problem, an appropriate degree of accuracy"
canonical: https://lightmysky.com/learn/mathematics/estimation-to-check-answers-to-calculations-mt_ilPrU0cbtT
source: https://lightmysky.com/learn/mathematics/estimation-to-check-answers-to-calculations-mt_ilPrU0cbtT.md
retrieved: 2026-10-19
---

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# Estimation to check answers to calculations

Use estimation to check answers to calculations and determine, in the context of a problem, an appropriate degree of accuracy

Subject: Mathematics · Area: Multiplication & Division · Ages 10 to 11
Page: https://lightmysky.com/learn/mathematics/estimation-to-check-answers-to-calculations-mt_ilPrU0cbtT

## Ready when they can

- Estimate 487 × 23 by rounding to 500 × 20 and use this to check a calculated answer
- Determine whether an exact answer or an estimate is more appropriate in a given context
- Spot an unreasonable answer by comparing with a quick mental estimate

## Lesson: Estimating to check your answers

You already know how to round numbers to make a quick estimate. Now you'll use that same idea to check your calculations, especially when you multiply or divide bigger numbers.

*(drawing: Rounding first keeps the maths easy. 642 is closer to 600 than to 700, so it rounds down to 600.)*

**Example.** To estimate 487 x 23, round each number first: 487 rounds to 500, and 23 rounds to 20. So 500 x 20 = 10,000 is your estimate. The exact answer is 11,201. Since 11,201 is close to 10,000, the exact answer looks about right.

Sometimes you need the exact answer, and sometimes an estimate is enough. If you're working out exact change or exact money, you need the precise number. If you just want a rough idea, like roughly how much paint to buy, an estimate does the job.

**Tip.** If your worked-out answer is way off from your estimate, like ten times too big or too small, check your work. A missing digit or a slipped decimal point is often the cause.

**Recap.** Round first to make an estimate, then check your exact answer against it, and decide whether the situation needs exact or roughly right.

## Practice

18 questions on this page, each with its working shown.

## Needs first

- [Rounding to a required degree of accuracy](https://lightmysky.com/learn/mathematics/rounding-to-a-required-degree-of-accuracy-mt__casygEB85)
- [Checking Answers by Rounding](https://lightmysky.com/learn/mathematics/checking-answers-by-rounding-mt_G3sVFQNCme)

## Opens up

- [Rounding Answers](https://lightmysky.com/learn/mathematics/rounding-answers-mt_QU5R7Aajy9)