D&F: Multiplying Decimals Cont’d


When we multiply decimals it’s usually easier to turn them into ordinary numbers first. We do this by simply multiplying them by numbers of 10,100,1000 etc. This allows us to do normal multiplication. When we find out the answer, we reverse the process to find out the final answer.

Example 1

To make it an ordinary number we need to multiply 0.7 by 10 which equals 7.

We then do 5 × 7 = 35

Now reverse the process: Divide 35 by 10, making the final answer 3.5

Example 2

To make it an ordinary number we need to multiply 0.07 by 100 which equals 7.

We then do 6 × 7 = 42

Now reverse the process: Divide 42 by 100, making the final answer 0.42

Example 3

To make it an ordinary number we need to multiply 2.7 by 10 which equals 27.

We then do 5 × 27 = 135

Now reverse the process: Divide 135 by 10, making the final answer 13.5

Example 4

 

When multiplying two decimals the process is slightly different. Both numbers need to be divided by 10 × 10 = 100

To make it an ordinary number we need to multiply both numbers by 10 and 5 × 3 = 15

Now reverse the process: Divide 15 by 100, making the final answer 0.15

Example 5

When multiplying two decimals the process is slightly different. Both numbers need to be divided by 10 × 100 = 1000

To make it an ordinary number we need to multiply both numbers by 10 and 100 and 6 × 8 = 48

Now reverse the process: Divide 48 by 1000, making the final answer 0.048