ST361 HW4 (due Thursday, 9/26/09)
(a) Show your work in order to earn the full credit. This means that you have to present your
steps or explain your reasoning for the answers you obtain, rather than just to write down the
answer itself.
Note that answers without steps or reasoning will receive 0 credits even if the answers are
(b) Remember to staple your homework and write your name on your homework. You’ll
lose 5 points if not.
1) 5.26 (p.221) Do (a) only
2) 5.28 (p.221)
3) Let x denote the amount of time for which a book on 2-hour reserve at a college-library is
checked out by a randomly selected student and suppose that the density function of X
.5 x
f ( x)  
0 x2
(a) Draw the density curve, and verify that f(x) is a legitimate distribution (i.e., verify that
the total area under f(x) is 1).
(b) Calculate the probability that the book is checked out for less than an hour.
4) 1.19 (p.31)
(b) (Note that “long run proportion” means “probability” here.)
5) 1.26 (p.32) (Note that “long run proportion” means “probability” here.)