I have the following question:
$10$% of applications for a job possess the right skills. A company has 3 positions to fill and they interview applicants one at a time until they fill all $3$ positions. The company takes $3$ hours to interview an unqualified applicant and $5$ hours to interview a qualified applicant. Calculate the mean of the time to conduct all interviews.
I got a bit lost considering that they wanted to mean of all interviews however I just did $0.10*3+0.90*5=3.2$ which seemed too simplistic, any help in correction/verification would be appreciated.