Operations with Decimals

.Addition/Subtraction of Decimals: To add or subtract decimal numbers, the numbers must be aligned so that their like place values may be added to one another.  The easiest way to do this is to “line up” the decimal points.

For example:

Adding 12.35 and 5.2. Notice how the decimal points are lined up.

           + 5.20

Subtracting 2.28 from 12.993. Notice how the decimal points are lined up.

          –  2.280

Multiplication/Division of Decimals:  When multiplying numbers with decimals, first multiply them as if they were whole numbers. Next, decide the placement of the decimal in the resulting product by summing the total number of decimal places of the numbers being multiplied.

For example, if you multiply 2.3 times 4.5, each number has one digit to the right of the decimal, so each has one decimal place. When they are multiplied, the result will have two digits to the right of the decimal, or two decimal places.


To determine how many digits are to the right of the decimal point in the result, count the decimal places in the two numbers being multiplied and add these together.


For the division of decimals, the divisor should be a whole number.

If the divisor has a decimal in it, make it a whole number by moving the decimal point the appropriate number of places to the right.


If the decimal point is shifted to the right in the divisor, it must also be shifted for the dividend the equivalent number of places.


Once the decimal point is moved so the divisor is a whole number, traditional division can be performed.


General Algebra Tips

The views and opinions expressed in this page are strictly those of Mary Lou Baker.
The contents of this page have not been reviewed or approved by Columbia State Community College.

This page was edited on 28-Jan-2013