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Estimating solutions by rounding to significant figures is a crucial mathematical skill, particularly for GCSE, IGCSE, and Key Stage 3 students. This technique simplifies complex calculations, making it easier to quickly assess the reasonableness of answers.

**Significant Figures:** The most important digits in a number, starting from the first non-zero digit.

**Rounding Rules:** Round up if the next digit is 5 or greater; round down if it’s less than 5.

**Simplified Calculations:** Use rounded numbers to estimate solutions, streamlining arithmetic operations.

Making Approximations using Rounding

Key Stage 3 Lesson

Estimating Solutions by Rounding

GCSE/IGCSE Lesson

Extended Learning

Problem Solving Lesson

Revision Lesson

Revision Lesson

**Why is estimation important in exams?**

It saves time and helps verify detailed calculations.

**How many significant figures should be used?**

Typically, one or two significant figures are sufficient for estimation.

Estimating by rounding to significant figures is beneficial in algebra, geometry, and data analysis. It helps approximate values, simplify complex problems, and verify results’ accuracy.

This technique is widely used in various fields such as engineering, physics, and finance. Engineers estimate materials needed for construction, and financial analysts approximate costs and profits.

Misidentifying significant figures is a common error, particularly when it involves leading zeros, which are not considered significant. Another frequent mistake is incorrect rounding; it is essential to always consider the digit immediately to the right of your rounding point to ensure accuracy. Additionally, over-reliance on estimation can lead to problems; while estimation is a useful tool for checking calculations, it should never be used as a substitute for precise calculations.

**Question 1**

For a music concert,

297 tickets were sold for £9.60 each.

396 tickets were sold for £19.75 each.

Work out an estimate for the total amount of money paid for these tickets.

**Question 2**

Work out an estimate for

\frac{5.8 \times 8.15}{0.29}

**Question 3**

Clare drives a distance of 497 kilometers on a motorway in Italy.

She pays 0.78 euros for every 10 kilometers she drives.

(a) Work out an estimate for the total amount that Clare pays.

(b) Is your answer to part (a) an underestimate or an overestimate?

Give a reason for your answer.

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