The report "undergraduate students and credit cards in 2004: an analysis of usage rates and trends" (nellie mae, may 2005) estimated that 21% of undergraduates with credit cards pay them off each month and that the average outstanding balance on undergraduates’ credit cards is $2169. these estimates were based on an online survey that was sent to 1260 students. responses were received from 132 of these students. is it reasonable to generalize the reported estimates to the population of all undergraduate students? address at least two possible sources of bias in your answer.

An automobile assembly line operation has a scheduled mean completion time, μ, of 12 minutes. the standard deviation of completion times is 1.6 minutes. it is claimed that, under new management, the mean completion time has decreased. to test this claim, a random sample of 33 completion times under new management was taken. the sample had a mean of 11.2 minutes. assume that the population is normally distributed. can we support, at the 0.05 level of significance, the claim that the mean completion time has decreased under new management? assume that the standard deviation of completion times has not changed.