At Franklin High School, 15% of students play basketball and 4% play baseball and basketball. What is the probablity that a student plays baseball given that he or she plays basketball?

There is a formula to use for this kind of problem (what is A given B).

P (A | B) = [P (B ∩ A) ] / P (B) which says the probability of A given B equals the probability of B and A over the probability of B. So if you make baseball A and basketball B you can plug them into the equation:

P (A | B) = 0.04 / 0.15

When you solve I think you should get 27%