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Example

Adding 712+518\frac{7}{12} + \frac{5}{18}

Add two fractions whose denominators differ by finding the LCD and converting to equivalent fractions:

712+518\frac{7}{12} + \frac{5}{18}

Step 1 — Find the LCD and rewrite: Factor each denominator: 12=22312 = 2 \cdot 2 \cdot 3 and 18=23318 = 2 \cdot 3 \cdot 3. The LCD is 2233=362 \cdot 2 \cdot 3 \cdot 3 = 36. The denominator 1212 is missing one factor of 33, so multiply the first fraction by 33\frac{3}{3}; the denominator 1818 is missing one factor of 22, so multiply the second fraction by 22\frac{2}{2}:

73123+52182=2136+1036\frac{7 \cdot 3}{12 \cdot 3} + \frac{5 \cdot 2}{18 \cdot 2} = \frac{21}{36} + \frac{10}{36}

Step 2 — Add: Combine the numerators over the common denominator: 21+1036=3136\frac{21 + 10}{36} = \frac{31}{36}.

Step 3 — Simplify: Because 3131 is prime, it shares no factor with 3636, so the result is already in simplest form.

Important: do not simplify the equivalent fractions before adding — doing so would undo the common denominator and return the original fractions.

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Updated 2026-05-02

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