In a group of 800 people, 1/5 play at least one instrument, 128 play two or more. What is the probability that one student play exactly one instrument?  Choose one:  A) 2/125  B) 3/125  C) C)2/25  D) 3/25  E) 1/25
P(playing 2 or more instruments) = 128/800 = 4/25.   Then, the probability of playing exactly one instrument is given by:   P(playing 1 or more instruments) - P(playing 2 or more instruments) = 1/5 - 4/25 = 1/25.   Answer 1/25.
<result>E</result>
In a group of 800 people, 1/5 play at least one instrument, 128 play two or more. What is the probability that one student play exactly one instrument?