shinna wrote:

At a certain school 25% of the students join a band, 25% play a sport and 20% both join the band and play a sport. if a randomly selected student is a member of the band, what is the probability that the student also plays a sport?

A. 3/4

B. 1/5

C. 2/5

D. 1/2

E. 4/5

We can let the number of students = 100.

We know that 25 join the band, 25 play a sport and 20 do both.

We are told that a randomly selected student is a band member, so we consider only the 25 students who are band members. Of those 25, we know that 20 play a sport. Thus, the probability that a student plays a sport, given that he joins a band is 20/25 = 4/5.

Answer: E

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