When do students need to find the least common multiple?

Finding the least common multiple (LCM) is essential when adding fractions with unlike denominators. To add fractions, the denominators must be the same, which often requires finding a common denominator. The LCM of the denominators provides the smallest number that each of them can divide into evenly, allowing the fractions to be rewritten with the same denominator. This process enables accurate addition of the numerators.

In contrast, adding fractions with unlike numerators does not directly relate to the need for finding an LCM; rather, it still requires a common denominator, which is where the LCM comes into play. Multiplying fractions does not necessitate a common denominator at all, as multiplication of fractions operates independently of the denominators; thus, it is not applicable in cases involving LCM.