On a university campus, 40% of the students are Microsoft fans, while the other
ID: 3064546 • Letter: O
Question
On a university campus, 40% of the students are Microsoft fans, while the other 60% are
Apple fans. The campus bookstore wants to sell a printer to the students. It is known that
75% of the Microsoft fans would buy the printer, while only 30% of the Apple fans would
buy the printer.
a) The businessman randomly picks a student on this campus, what is the probability
that he/she would buy the printer?
b ) John, a student at this university, has purchased the printer. What is the probability
that he is an Apple fan?
Explanation / Answer
(a)
Buy printer Not buy printer Total
Microsoft 0.40X0.75 = 0.30 0.40X0.25 = 0.10 0.40
Apple 0.60X0.30=0.18 0.60X0.70=0.42 0.60
Total 0.48 0.52 1.00
P(Buy printer) = 0.48
(b)
P(Apple/Buy printer) = P(Apple & Buy printer)/P(Buy printer)
= 0.18/0.48 = 0.375