To subtract the fractions \( \frac{7}{8} \) and \( \frac{1}{2} \), we first need a common denominator. The denominator for \( \frac{7}{8} \) is \( 8 \), and for \( \frac{1}{2} \), we need to convert it to eighths.
Convert \( \frac{1}{2} \) to eighths:
\[ \frac{1}{2} = \frac{1 \times 4}{2 \times 4} = \frac{4}{8} \]
Now we can perform the subtraction:
\[ \frac{7}{8} - \frac{4}{8} = \frac{7 - 4}{8} = \frac{3}{8} \]
The answer as a fraction is \( \frac{3}{8} \).
Thus, the numerator is:
\[ \boxed{3} \]