D&F: Multiplying Decimals

There are a few rules that help us to multiply with decimals and when we multiply with decimals it is usually easier to change the decimals into ordinary numbers

How do we do this?  We simply multiply by powers of 10

In other words, we are going to change our decimals into whole numbers by multiplying by either 10, 100, 1000 etc, this then allows us to do normal multiplication

Finally, when we have found an answer, we reverse the multiplying by powers of 10 process for each time to get back to the original answer

Hence, we are simply using powers of 10 to allow us to do simpler calculations and then reversing the process to get the actual answers

Example 1

We have 5 times 0.7

We can say that it is 5 times 7 because we can first multiply the 0.7 by 10 to make it 7

We then get a simple answer of 35

And now remember, we need to reverse the times 10 by dividing by 10, therefore, the actual answer is 3.5

Let us take a look at some slightly more difficult examples

Example 2

We can do exactly same thing that we have done before, turning decimals into whole numbers, then doing normal multiplication, getting an answer and then reversing the original multiplication power of 10

We have 6 times 1.12

We can multiply 1.12 by 100 to turn it into a whole number

Then multiply it by 6 to get 672

But remember to reverse the multiplication by 100 that we did above by dividing by 100 to get the actual answer of 6.72