IXL | Least common denominator

What
is
the
least
common
denominator
of
1
6
and
5
9
?

ref_doc_title.

Learn with an example

question

What
is
the
least
common
denominator
of
1
4
and
7
12
?

key idea

The least common denominator is the least common multiple of the denominators.

solution

The denominators are 4 and 12. Find the least common multiple of 4 and 12.

Write the prime factorization for each number.

4 = 2 × 2
12 = 2 × 2 × 3

Repeat each prime factor the most number of times it appears in any of the prime factorizations above.

The most the factor 2 appears is twice.

The most the factor 3 appears is once.

So, multiply:

2 × 2 × 3 = 12

The least common multiple of 4 and 12 is 12.

The least common denominator of

1
4
and
7
12

is 12.

Looking for more? Try these:

Lesson: Least common denominator

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Teacher tools

Work it out

Not feeling ready yet? These can help:

J.5Least common denominator

F.8Least common multiple

J.2Equivalent fractions

F.9Least common multiple of three or four numbers

Lesson: Least common denominator

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