To express 4:12 as a fraction, you can write it as \( \frac{4}{12} \).
You can simplify this fraction by finding the greatest common divisor (GCD) of 4 and 12, which is 4:
\[ \frac{4 \div 4}{12 \div 4} = \frac{1}{3} \]
So, 4:12 as a fraction in simplest form is \( \frac{1}{3} \).