Multiplying decimals
Multiplying decimals works the same way as multiplying whole numbers.
So, if the question includes one decimal place in total, \(3.2 \times 6\), then the answer must include one decimal place, 19.2. If the question has two decimal places in total, \(4.2 \times 2.8\), then the answer must have two decimal places, 11.76.
Example
What is \(3.72 \times 2.3\)?
First, do the calculation with whole numbers, so work out \(372 \times 23\)
Note that there are three decimal places in the calculation (3.72, 2.3), so there needs to be three decimal places in the answer. The answer is therefore 8.556.
Question
What is \(5.2 \times 8\)?
First, work out \(52 \times 8\).
Next, note the number of decimal places in the question - just one - and make sure that there is an equal number of decimal places in the answer.
The answer is therefore: 41.6
Remember, if your answer has zeros in the decimal places then you must count these too.
Question
What is \(3.4 \times 5.5\)?
First, work out \(34 \times 55\).
As before, note the number of decimal places in the question - two - and make sure that there is an equal number of decimal places in the answer.
The answer is therefore 18.70 which would be written as: 18.7