# 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? |