試題詳解

24. (5%) There are 2 exams in Statistics class. The midterm score (X) is approximately normal distributed with mean 60 and standard deviation 20. The final exam score (Y) is approximately normal distributed with mean 80 and standard deviation 10. The overall score is the weighted average of two scores: Z = X * 40% + Y * 60%. Suppose that cor(X, Y) = 0.6. Which of the following statement is FALSE?
(A) The overall score has a mean 72
(B) The overall score has a standard deviation 14
(C) Emily got 60 in the midterm. The expected score for her final exam is 80
(D)cor(Z,X) >0.6
(E) The overall score is approximately normally distributed