February 4th

February 4th

Adding and Subtracting Fractions

Before you start adding and subtracting fractions, you should know how to find the lowest common denominator of at least two fractions. You need to find a common denominator in order to express the fractions being added or subtracted in the same proportions.

Example #1:

In the fractions , the lowest common denominator is 15. This is the lowest number that is a multiple of both 3 and 5.

Example #2:

Now let's add the fractions:

Whatever we multiply the denominators by, we must multiply the numerators by.

Example #3:

Let's subtract fractions:

Whatever we multiply the denominators by, we must multiply the numerators by.

Example #4:

The common denominator is 8. Why isn’t it 4? 2?