To express the statement "5 is to 1 as 20 is to 4" as a proportion in fractional notation, we want to write it in the form:
\[ \frac{5}{1} = \frac{20}{4} \]
Among the responses you provided, the correct proportional notation is:
\[ \frac{5}{1} = \frac{20}{4} \]
So the correct answer is:
\( \frac{5}{1} = \frac{20}{4} \)