Example

Example of Contrasting Subtraction and Multiplication of rac{3a}{4} and rac{8}{9}

This example contrasts the procedures for subtracting and multiplying the fractions rac{3a}{4} and rac{8}{9}. The first step is to identify the operation, which determines whether a common denominator is needed.

ⓐ Subtracting rac{3a}{4} - rac{8}{9}: Subtraction requires a least common denominator (LCD). The LCD for 44 and 99 is 3636. First, rewrite each fraction as an equivalent fraction with the LCD: rac{3a \cdot 9}{4 \cdot 9} = rac{27a}{36} and rac{8 \cdot 4}{9 \cdot 4} = rac{32}{36}. Then, subtract the numerators and place the difference over the common denominator: rac{27a - 32}{36}. Because there are no common factors to remove between the numerator and denominator, this expression is fully simplified.

ⓑ Multiplying rac{3a}{4} \cdot rac{8}{9}: Multiplication does not require a common denominator. We simply multiply the numerators and denominators: rac{3a \cdot 8}{4 \cdot 9}. Before multiplying out, rewrite showing common factors: rac{3a \cdot 2 \cdot 4}{4 \cdot 3 \cdot 3}. Removing the common factors of 33 and 44 from both the numerator and denominator simplifies the expression to rac{2a}{3}.

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Updated 2026-04-21

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