To write "5 is to 1 as 20 is to 4" in fractional notation, we can express it as:
\[ \frac{5}{1} = \frac{20}{4} \]
Thus, the correct response is:
51=204 start fraction 5 over 1 end fraction equals start fraction 20 over 4 end fraction.
This shows that the ratios are equal, in line with the statement.