Subject: mathqa
Question: 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 , 5 of whom are females , by how much does the index for the females exceed the index for the males in the group ?
Option: 
A: 0.25
B: 0.5
C: 0.0625
D: 0.6
Answer: B