Twenty students out of 80 kids had pizza for lunch. What is the percentage of students that had pizza for lunch? Please help!!!

Ineed in figuring out this problem.

What is the lcm of 16 and 40 ? 24 and 40 ?

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.