Like-denominator fractions represent quantities partitioned into the same-sized parts, so their sum combines the counts of those parts while preserving the common denominator; the result may be rewritten as an equivalent fraction in simplest form or as a mixed number when it exceeds one. Number lines and fraction bars show why denominators are not added, a common misconception, and connect the operation to composing a whole. This scope excludes addition with unlike denominators and the more general use of common denominators required for it.
When fractions have the same denominator, they are made of the same-sized parts. Add the numerators, which tell how many parts there are, and keep the denominator.
Example:
So, the answer is .
Do not add the denominators. The pieces are still eighths, not sixteenths. You are combining the number of same-sized pieces, just as combining eighth-size pieces with eighth-size pieces gives eighth-size pieces.
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