Cho hình chóp S ABCD . Có đáy là hình chữ nhật, cạnh AB b = , BC b = 3 , SA vuông góc với mặt phẳng đáy. Góc giữa cạnh bên SC và mặt phẳng đáy bằng 45Ο . Khoảng cách từ điểm A đến mặt phẳng ( ) SBD tính theo b bằng A. 2 5 . 5 b B. 2 5 . 3 b C. 2 57 . 19 b D. 2 57 . 3

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.