Year 8 Interactive Maths - Second Edition

Multiplication of Decimals

• Ignore the decimal points and multiply the digits.
• Then count the number of decimal places in each of the numbers being multiplied which will be the total number of decimal places in the answer.
• Use this total number of decimal places to place a decimal point in the answer.

Example 11

Calculate 0.8 × 0.9.

Solution:

Note:

• There is 1 decimal place in 0.8 and 1 decimal place in 0.9 and thus, 2 decimal places in the answer.
• First ignore the decimal points and multiply 8 by 9.  Then include the 2 decimal places in the answer.

Example 12

Calculate 0.78 × 0.5.

Solution:

Note:

• There are 2 decimal places in 0.78 and 1 decimal place in 0.5 and thus, 3 decimal places in the answer.
• First ignore the decimal points and multiply 78 by 5.  Then include the 3 decimal places in the answer.

Example 13

Calculate 3.24 × 0.67.

Solution:

Note:

• There are 2 decimal places in 3.24 and 2 decimal places in 0.67 and thus, 4 decimal places in the answer.
• First ignore the decimal points and multiply 324 by 67.  Then include the 4 decimal places in the answer.