The easiest way to solve this problem is to make a table, based on 100 total person
Prefer week ends Prefer week days Total
Female 10 55 65
Male 15 20 35
Total 25 75 100
The bold numbers are conclusions. The plain numbers are data.
The probability that a randomly selected club member is female, given that that person prefers swimming on weekends is [10 / 25] = 0.40
Answer: option D. 0.40