Chapter 1 - Introduction to Algebraic Expressions - 1.3 Fraction Notation - 1.3 Exercise Set - Page 27: 58

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$\frac{11}{12}\times\frac{12}{11}=\frac{11\times12}{12\times11}=\frac{121}{121}$ The numerator and denominator have a common factor of 121. Therefore, $\frac{121}{121}=\frac{121\div121}{121\div121}=\frac{1}{1}=1$. In general, the product of a number and its reciprocal will be 1.