Slobodanka

middle grade 8th

What is a Common Denominator?

Thanks

Hi Slobodanka,
We say that two fractions have a **common denominator** if both fractions have the same denominator. This is important when you add or subtract two fractions. For example if you want to add ^{3}/_{4} and ^{1}/_{6} you need first to exprress both fractions with the same denominator. That is you need to find a common denominator.

A denominator that will work is 12 since

^{1}/_{6} = ^{2}/_{12}
and
^{3}/_{4} = ^{9}/_{12}
Thus

^{1}/_{6} + ^{3}/_{4}

= ^{2}/_{12} + ^{9}/_{12}

= ^{11}/_{12}
**How did I know that 12 is a common denominator?**

The denominators of the two original fractions are 4 and 6 and what I noticed is that 12 is a multiple of both 4 and 6. This means that I can express both fractions with a denominator of 12.
I hope this hepls,

Penny