Chapter 5 - Number Theory and the Real Number System - 5.3 The Rational Numbers - Exercise Set 5.3 - Page 285: 73

$\dfrac{ 2 }{ 3 }$

To combine fractions, make sure that the fractions have the same denominators before combining their numerators. \begin{align} \dfrac{ 5 }{ 6 } - \dfrac{ 1 }{ 6 } &= \dfrac{ 5 - 1 }{ 6 } &&\text{Subtract the numerators} \\ &= \dfrac{ 4 }{ 6 } \\ &= \dfrac{ 4 \div 2 }{ 6 \div 2 } &&\text{Reduce to lowest terms} \\ &= \boxed{ \dfrac{ 2 }{ 3 } } \end{align}