In addition and subtraction of fractions, why is it important to know the least common denominator?

Knowing the least common denominator (LCD) is essential in the addition and subtraction of fractions because it allows you to express fractions with different denominators as equivalent fractions with a common denominator. This common denominator is needed to ensure that the fractions can be accurately combined. When adding or subtracting, the denominators must be the same so that you can directly add or subtract the numerators.

Using the LCD simplifies the process of fraction addition and subtraction by providing a clear method for transforming all involved fractions into a form that is compatible for these operations. This understanding and capability enable students to effectively solve problems involving fractions and to compare them when necessary.

In contrast to the other options, knowing the least common denominator does not simply serve to compare fractions (which is certainly a benefit), nor is it focused on the simplification of fractions or making them equal. Rather, its primary purpose is to allow for the necessary alignment of fractions that are being added or subtracted. Additionally, the least common denominator is not limited to whole numbers, as it is a fundamental concept that specifically applies to rational numbers, including fractions.