Convert the mixed numbers to improper fractions:

$2\tfrac{1}{8} = \frac{17}{8}, \quad 4\tfrac{1}{4} = \frac{17}{4}$

Divide by multiplying by the reciprocal:

$\frac{17}{8} \div \frac{17}{4} = \frac{17}{8} \times \frac{4}{17} = \frac{4}{8} = \frac{1}{2}$