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Definition

Least Common Denominator

The least common denominator (LCD) of two or more fractions is the least common multiple (LCM) of their denominators. It represents the smallest positive number that every denominator divides into evenly, making it the ideal shared denominator for rewriting fractions before adding or subtracting them. For instance, the LCD of 512\frac{5}{12} and 718\frac{7}{18} is 3636, because the LCM of 1212 and 1818 is 3636. Any technique used to find an LCM — such as listing multiples or using prime factorizations — can be applied to find the LCD by working with the denominators of the given fractions.

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Updated 2026-05-02

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