Se construyó una alberca de 20 m de largo por 12 metros de ancho y alrededor de ella quiere instalar azulejo antiderrapante si la superficie del azulejo debe ser de 144 metros cuadrados ¿qué ancho debe tener la superficie azulejo?

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.