Answer
$\dfrac{25}{6}$
Work Step by Step
RECALL:
(1) $\dfrac{\frac{a}{b}}{\frac{c}{d}}=\dfrac{a}{b} \div \dfrac{c}{d}$
(2) $\dfrac{a}{b} \div \dfrac{c}{d} = \dfrac{a}{b}\cdot \dfrac{d}{c}$
Use the rules above to obtain:
$\dfrac{5}{21} \div \dfrac{2}{35}
\\=\dfrac{5}{21} \cdot \dfrac{35}{2}$
Cancel the common factor, $7$, and then simplify to obtain:
$\require{cancel}
=\dfrac{5}{\cancel{21}3} \cdot \dfrac{\cancel{35}5}{2}
\\=\dfrac{5}{3} \cdot \dfrac{5}{2}
\\=\dfrac{5(5)}{3(2)}
\\=\dfrac{25}{6}$