Question

Of all the Sunny Club members in a particular city, 25% prefer swimming on weekends and 75% prefer swimming on weekdays. 10% of the members in the city prefer swimming on weekends and are female. 55% of the members in the city prefer swimming on weekdays and are female. What is the probability that a randomly selected club member is female, given that the person prefers swimming on weekends? (A).19, (B).20, (C).24, (D).40, (E).55

Answer 1

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