機率論的兩個問題

1.Let X be a random variable with pmf P(X) = c/x^3 if x =1,2,3,...
0 otherwise
(a) Find the cdf of X
(b) Does the expectation exist? Find it if it does exist.
(c) Does the variance exist? Why?
2.Deer ticks can be carriers of either Lyme disease or human granulocytic
ehrlichiosis(HGE). Based on a recent study, suppose that 16% of all ticks
in a certain location carry Lyme disease,10% carry HGE,and 10% of the
ticks that carry at least one of these diseases in fact carry both of them.
If a randomly selected tick is found to have carrier HGE,what is the
probability that the selected tick is also a carrier of Lyme disease?