To write the statement "5 is to 1 as 20 is to 4" in fractional notation as a proportion, you use the format:
\[ \frac{5}{1} = \frac{20}{4} \]
So the correct way to express this in fractional notation is:
\[ \frac{5}{1} = \frac{20}{4} \]
Therefore, the response you are looking for is:
start fraction 5 over 1 end fraction equals start fraction 20 over 4 end fraction.