Sometimes fractions have different denominators. These are called unlike fractions. When adding or subtracting fractions with unlike denominators, it is necessary to find a common denominator to get the correct answer. This is the same process as finding the least common multiple.
Example 1/30 + 1/42
Factor them.
2 x 3 x 5 = 30
2 x 3 x 7 = 42
Combine the factors, eliminating duplicates.
2 x 3 x 5 x 7 = 210, the lowest common denominator.
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The least common denominator is the least common multiple of the denominators of the fractions.
A common denominator is needed when adding or subtracting fractions of different denominators.
They are essentially the same. A common denominator is the common multiple of a set of denominators of a set of fractions.
You need at least two numbers to find a common denominator.
It is infinity but the lowest common denominator is 3185