What is meant by the lowest common denominator?

Answer 1

Finding The Least Common Denominator

The least common denominator of two or more non-zerodenominators is actually the smallest whole number that is divisible by each of the denominators. Actually, this is the same basic idea behind finding the Least Common Multiple (LCM) for whole numbers (without the fractional parts).

To find the least common denominator, simply list the multiples of each denominator (multiply by 2, 3, 4, etc.) then look for the smallest number that appears in each list.

Example: Suppose we wanted to add 1/5 + 1/6 + 1/15. We would find the least common denominator as follows...

• First we list the multiples of each denominator.

Multiples of 5 are 10, 15, 20, 25, 30, 35, 40,...

Multiples of 6 are 12, 18, 24, 30, 36, 42, 48,...

Multiples of 15 are 30, 45, 60, 75, 90,....

• Now, when you look at the list of multiples, you can see that 30 is the smallest number that appears in each list.

• Therefore, the least common denominator of 1/5, 1/6 and 1/15 is 30.

This method works pretty good. But, in adding fractions with larger numbers in the denominators can get pretty messy. Again, see the Related Link for another way to find a least common denominator.