# Estimate Calculations By Rounding to One Significant Figure

In this worksheet, students will round numbers to one significant figure in order to estimate the answer to a calculation.

Key stage:  KS 3

Curriculum topic:   Number

Curriculum subtopic:   Round/Approximate Numbers Appropriately

Difficulty level:

#### Worksheet Overview

In this activity, we will be using our rounding skills to estimate the answers to calculations.

This skill is useful for when we need to make approximate calculations for when we don't have a calculator.

Engineers use this skill to estimate the quantity of materials needed for a building.

We also use rounding when trying to find out what our shopping bill may be as we are going around the supermarket!

Example 1

Round off the values in the calculation to 1 significant figure to work out an estimate to the calculation below.

7.91 + 8.3 + 10.6

First, let's round each value to 1 sig. fig.

7.91: the 1 significant figure we need is the 7. We look at the digit before the 7, which is a 9. This means that it rounds the 7 up to 8.

8.3: the 1 significant figure we need is the 8. We look at the digit before the 8, which is a 3. This means that it rounds down to keep it as 8.

10.6: the 1 significant figure we need is the 1. We look at the digit before the 1, which is a 0. This means that it rounds down to keep it as 1. However, we have to include a zero as a place holder because the number 1 is not the same as the number 10!

This gives us:

7.91 → 8

8.3 → 8

10.6 → 10

Now we have our rounded values, we can find an estimate for the calculation.

8 + 8 + 10

= 26

Example 2

Round off the values in the calculation to 1 significant figure to work out an estimate to the calculation below.

(7.91 + 8.3 ) ÷ 10.1

First, let's round each value to 1 sig. fig.

7.91 → 8

8.3 → 8

10.1 → 10

Now we have our rounded values, we can find an estimate for the calculation.

(8 + 8) ÷ 10

= 16 ÷ 10

= 1.6

Great ... let's try the activity!

### What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started