# What is the lowest common denominator for 1/4, 3/5, and 7/9?

Mar 29, 2016

Lowest Common Denominator is $21$

#### Explanation:

Lowest Common Denominator of fractions is different from finding Lowest Common Denominator of natural numbers.

To find the Lowest Common Denominator of fractions,

one has to first find the Lowest Common Denominator of all the numerators, say it is $A$

and then Highest Common Factor of all the denominators, say it is $B$

Then $\frac{A}{B}$ is the Lowest Common Denominator of fractions.

In the given example, we have $1$, $3$ and $7$ as numerator and as there is no common factor between them, we can multiply them to get their Lowest Common Denominator, which is $21$ .

In the denominators we have $4$, $5$ and $9$ and again we do not have any common factor between which divides all these numbers and hence Highest Common Factor is $1$.

Hence, Lowest Common Denominator of fractions $\frac{1}{4}$, $\frac{3}{5}$ and $\frac{7}{9}$ is $\frac{21}{1}$ or $21$.