For a group of n people, k of whom are of the same sex, the (n-k)/n expression yields an index for a certain phenomenon in group dynamics for members of that sex. For a group that consists of 20 people, 8 of whom are females, by how much does the index for the females exceed the index for the males in the group?  Choose one
A) 0.05
B) 0.0625
C) 0.2
D) 0.25
E) 0.6

Rationale: index for females = ( 20 - 8 ) / 20 = 3 / 5 = 0.6 index for males = ( 20 - 12 / 20 = 2 / 5 = 0.4 index for females exceeds males by 0.6 - 0.4 = 0.2 answer : c
Answer: C