Estimate 0.48 × 812

Step by step

The question

Question: estimate 0.48 × 812.

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.

0.48: the first figure is 4.

The next digit is 8, 5 or more, so we round up: 0.5.

812: the first figure is 8.

The next digit is 1, 4 or less, so we round down: 800.

2 Work it out

So the answer is about 0.5 × 800.

Now it is easy to work out.

Careful!

We changed the numbers.

So we write ≈, about, not =.

0.5 times 800 is 400.

To multiply decimals: first 5 times 800, as whole numbers.

That is 4000.

Then count the decimal places: 1.

So it is 400.

So the answer is about 400.

3 Check

Let's check with a calculator.

The exact answer is about 389.8.

That is close to 400.

So the estimate is good!

Let's look back.

First: round to 1 significant figure.

Then: work it out.

Last: check.