A certain list consists of 21 different numbers. If n is in the list and n is 5 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?
Choices.
A) 1/20
B) 1/6
C) 1/5
D) 4/21
E) 5/21
series : a1, a2....a20,n   sum of a1+a2+...+a20 = 20*x (x = average)   so, n = 5*x   Hence, a1+a2+..+a20+n = 25x   So, the fraction asked = 5x/25x = 1/5   Answer 1/5
<result>C</result>
A certain list consists of 21 different numbers. If n is in the list and n is 5 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?