Estimate 6.8 × 31.2

Step by step

The question

Question: estimate 6.8 × 31.2.

To estimate means to find about how big the answer is.

We make every number easy first.

1 Round to 1 significant figure

We round each number to 1 significant figure: only its first figure stays.

6.8: the first figure is 6.

The next digit is 8, 5 or more, so we round up: 7.

31.2: the first figure is 3.

The next digit is 1, 4 or less, so we round down: 30.

2 Work it out

So the answer is about 7 × 30.

Now it is easy to work out.

Careful!

We changed the numbers.

So we write ≈, about, not =.

7 times 30 is 210.

So the answer is about 210.

3 Check

Let's check with a calculator.

The exact answer is about 212.2.

That is close to 210.

So the estimate is good!

Let's look back.

First: round to 1 significant figure.

Then: work it out.

Last: check.