In arithmetic, decimal numbers play a big part. You should be able to do decimal multiplication without a calculator. All four operations; addition, subtraction, multiplication, and division can be done with decimal numbers.
Adding and subtracting decimal numbers is easy if you know the place value well. You just need to write in a way that decimal points of all numbers involve in addition or subtraction come in one column. Complete the addition or subtraction and the decimal point for the answer should go in the same column.
To multiply two decimal numbers, follow these steps:
- Write both numbers with their decimal points.
- Ignore the decimal points and multiply the numbers as if they were whole numbers.
- Count the total number of decimal places (the digits after the decimal point) in the two numbers being multiplied.
- Place the decimal point in the product so that there is the same number of decimal places as the total number of decimal places in the two numbers being multiplied.
For example, suppose we want to multiply 0.75 by 3.2. Ignoring the decimal points, we have:
075 x 32 = 240
There are 1 decimal place in 0.75 and 1 decimal place in 3.2, for a total of 2 decimal places. Therefore, we place the decimal point in the product as follows:
0.75 x 3.2 = 2.40
The result is 2.40.
Here’s another example. Suppose we want to multiply 0.012 by 0.0034. Ignoring the decimal points, we have:
12 x 34 = 408
There are 3 decimal places in 0.012 and 4 decimal places in 0.0034, for a total of 7 decimal places. Therefore, we place the decimal point in the product as follows:
0.012 x 0.0034 = 0.0000408
The result is 0.0000408.