At a high school, the probability that a student is a senior is 0.20. The
 probability that a student plays a sport is 0.15. The probability that a student
 is a senior and plays a sport is 0.05.
 What is the probability that a randomly selected student plays a sport, given
 that the student is a senior? 
 0.25
 0.15
 0.05
 0.33