Example

Adding 518+718\frac{5}{18} + \frac{7}{18}

Add two numerical fractions that share the denominator 1818, then simplify the result by factoring out common factors:

518+718\frac{5}{18} + \frac{7}{18}

Step 1 — Add the numerators over the common denominator. Since both fractions already share the denominator 1818, combine the numerators directly:

5+718=1218\frac{5 + 7}{18} = \frac{12}{18}

Step 2 — Factor the numerator and denominator to reveal common factors. Write 12=6212 = 6 \cdot 2 and 18=6318 = 6 \cdot 3:

6263\frac{6 \cdot 2}{6 \cdot 3}

Step 3 — Divide out the common factor. Cancel the shared factor of 66 from the numerator and denominator:

23\frac{2}{3}

This numerical example previews the same three-step procedure used for adding rational expressions with a common denominator: combine the numerators, factor completely, and simplify by removing common factors. The only difference when working with rational expressions is that the numerators and denominators are polynomials rather than plain numbers.

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Updated 2026-04-21

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Ch.8 Rational Expressions and Equations - Elementary Algebra @ OpenStax

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