Multiplying a decimal by a whole number
Multiplying a decimal by a whole number uses the same method as multiplying two whole numbers.
Question
Calculate:
a) \(2.43 \times 7\)
b) \(2.4 \times 5\)
a) There were two digits after the decimal point in the question \((4\) and \(3)\), so you must have two digits after the decimal point in the answer.
b) There was one digit after the decimal point in the question \((4)\), so you must have one digit after the decimal point in the answer. The answer is therefore \(12.0\). This can then be given as \(12\) unless you are asked to give an answer to 'one decimal place'. THis would mean keeping in one digit after the decimal point.
Remember:
- If there is one digit after the decimal point in the question, there will be one digit after the decimal point in the answer.
- If there are two digits after the decimal point in the question, there will be two digits after the decimal point in the answer.
In the above example you were asked to calculate \(2.4 \times 5\).
\({2}\times{5}={10}\) and \({3}\times{5}={15}\), so you are looking for an answer which is slightly higher than \({10}\). So an answer of \({12}\) seems correct.