What is the difference between a least common denominator and a least common multiple?  How important is it important to know and understand them? 

Difference between a least common denominator and a least common multiple

Answer 1 The least common denominator means the smallest number divisible by the denominators of all fractions in one set, and least common multiple means the smallest multiple that numbers have in common as product.

It is important to know the difference because for different equations we may have to use either one or the other. If we mix them up we can have a wrong result.

Answer 2: The lowest common denominator, or LCD, is the smallest number divisible by the denominators of every fraction in a set, and a least common multiple, or LCM, is the smallest multiple that two numbers have in common as products.

Important to know and understand them because we have many equations that are based on them, and we need to know the difference between these two.