6. The time taken, 7 minutes, for a special non-toxic paint to dry was measured for a random sample of 120 toys. The sample mean was 51.2 minutes and the unbiased estimate of the population variance is 37.4 minutes. Determine an 80% confidence interval for the mean drying time. 7. The librarian wishes to estimate the proportion of students who borrow 3 books at one time. She takes a random sample of 120 students and found that 33 of them borrowed books at one time. Find a 95% confidence interval for the true proportion of students who borrowed 3 books at a time. 8. The committee of a chess association wishes to make a change in the constitution. In order for this to happen, at least two-third of the adult members must vote for the change. Before the vote is taken, the secretary consults a random sample of 60 members and finds that 75% of the, will vote for the change. Calculate the 90% confidence interval for the proportion of all adult members who will vote for the change