21/25 + 1/2 =

\[\frac{21}{25} + \frac{1}{2} = \frac{21 \times 2}{25 \times 2} + \frac{1 \times 25}{2 \times 25} = \frac{42}{50} + \frac{25}{50} = \frac{42+25}{50} = \frac{67}{50} = 1\frac{17}{50}\]