Step by step
The question
Question: estimate 19.6 × 4.1 × 2.03.
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.
19.6: the first figure is 1.
The next digit is 9, 5 or more, so we round up: 20.
4.1: the first figure is 4.
The next digit is 1, 4 or less, so we round down: 4.
2.03: the first figure is 2.
The next digit is 0, 4 or less, so we round down: 2.
2 Work it out
So the answer is about 20 × 4 × 2.
Now it is easy to work out.
Careful!
We changed the numbers.
So we write ≈, about, not =.
20 times 4 is 80.
80 times 2 is 160.
So the answer is about 160.
3 Check
Let's check with a calculator.
The exact answer is about 163.1.
That is close to 160.
So the estimate is good!
Let's look back.
First: round to 1 significant figure.
Then: work it out.
Last: check.