Решение:
\[ \frac{1}{2} = \frac{1 \times 25}{2 \times 25} = \frac{25}{50} \]
\[ \frac{25}{50} - \frac{13}{50} = \frac{25 - 13}{50} = \frac{12}{50} \]
\[ \frac{12}{50} = \frac{12 \div 2}{50 \div 2} = \frac{6}{25} \]
Ответ: 6/25