A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average (arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?
~$\frac{1}{20}$~
~$\frac{1}{6}$~
~$\frac{1}{5}$~
~$\frac{4}{21}$~
~$\frac{5}{21}$~
average of the other 20 numbers