Estimate Calculations After Rounding to One Significant Figure

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

When dealing with large quantities, it's common to round or estimate the values. For instance, if you come across a football match attendance of 31,555, and someone asks you about the attendance, you might round it off to around 30,000. It's advisable to round to one significant figure.

When we shop at the supermarket, we often use rounding to estimate our total bill. To do this, we round the cost of each item to one significant figure.

Example 1

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

7.91 x 8.3 ÷ 2.11 

First, let's round each value to 1 significant figure.

7.91 → 8

8.3 → 8

2.11 → 2

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

8 x 8 ÷ 2  = 32

Example 2

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

(8.3  ÷  2.1) - 4.76

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

8.3 → 8

2.1 → 2

4.76 → 5

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

8 ÷ 2 = 4

4 - 5 = -1 

Great ... let's try the activity!