To add or subtract fractions, one must find which of the following first?

To add or subtract fractions, finding a common denominator is essential because it allows the fractions to be expressed in terms of the same size pieces. Without a common denominator, the fractions cannot be directly combined, as they represent different parts of a whole.

When the denominators of the fractions are the same, it is straightforward to add the numerators together while keeping the denominator constant, or to subtract the numerators if that is the operation being performed. For example, if you want to add 1/4 and 1/6, you first need to determine a common denominator. The least common multiple of the denominators 4 and 6 is 12, so you would convert each fraction: 1/4 becomes 3/12 and 1/6 becomes 2/12. Once converted, you can easily add them to get 5/12.

The other options, such as finding a common factor or least common multiple, do not directly facilitate adding or subtracting fractions. It’s the common denominator that allows for the fractions to be combined in a meaningful way, hence making it the crucial step in the process.