To convert 48% to an equivalent fraction with a denominator of 25, we first express it as a fraction:
\[ 48% = \frac{48}{100} \]
Next, we set up the equation:
\[ \frac{48}{100} = \frac{a}{25} \]
To find \(a\), we can use cross-multiplication:
\[ 48 \times 25 = 100 \times a \]
Calculating \(48 \times 25\):
\[ 48 \times 25 = 1200 \]
So we have:
\[ 1200 = 100a \]
Now, divide both sides by 100 to solve for \(a\):
\[ a = \frac{1200}{100} = 12 \]
Thus, the numerator \(a\) is
\[ \boxed{12} \]