Thinking Mathematically (6th Edition)

$\dfrac{2}{5}$
Reduce to lowest terms by factoring the numerator and the denominator and then cancelling common factors: $\require{cancel}=\dfrac{2(9)}{5(9)} \\=\dfrac{2\cancel{(9)}}{5\cancel{(9)}} \\=\dfrac{2}{5}$