MAT3172, Spring-Summer 2023 Probability Foundations
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
MAT3172, Spring-Summer 2023
Probability Foundations
Department of Mathematics and Statistics
Assignment 1, due on MAy 29,2023 at 11:59 in brightspace
Submission to my email or late submission will be ignored
1. Show that if H(x) > 0 is an increasing function of x then for a given random variable
X
E(H(X))
H(a) .
2. If X > 0 is an integer valued random variables. Prove that
-
X = I(X > n)
√=ò
and conclude that in this case
-
E(X) = P (X > n).
√=ò
3. Let F be a σ-field of subsets of Ω and suppose that B e F. Define
g = {A n B : A e F}
is a σ-field of subsets of B .
4. Prove
● (1) the Bonferoni’s inequality
P │ Ai ← > i1 P (Ai ) _ 1
● (2)
P │Ui Ai ← > 1 _ i P (Ai(c)).
5. Explain why
I │ni Ai ← = I(A1 ) + I(A2 )(1 _ I(A1 )) + I(A3 )(1 _ I(A1 ))(1 _ I(A2 )) + . . . .
Take expectation on both sides to generate a formula for P (ni Ai ) .
6. Assume P (X e [a, b]) = 1. Define the real valued function g(t) = E[(X _ t)2].
● (i) Find the minimizer of g and conclude that g(t) > Var(X).
Specially
g ╱ 、 > Var(X).
● (ii) Use part (i) and noticing that (X _ a)(X _ b) < 0 to conclude
(b _ a)2
4 .
7. Let X be a random variable such that, the moment generating function M(t) = E(et* ) < o, for t e (_h, h).
(i) Prove that
P (X > a) < e-at M(t), t e (0, h)
and
P (X < a) < e-at M(t), t e (_h, 0).
Conclude
P (X > a) < inf e-at M(t)
t<ò
when h = o.
(ii) For a random variable X the moment generating function M(t) exists for all t e R and
M(t) =
expìt/-expì -t/ 2t
1
if t 0
if t = 0,
show that
P (X > 1) = 0, P (X < _1) = 0.
8. The probability measure P is defined by
P (A) = exp(_x)dx.
A
If Ak = (2 _ 1/k, 3] u {5, 6}, for k = 1, 2, . . ., then find lim sup Ak and lim inf Ak and check if
lim P (A√ ) = P (lim A√ ).
2023-05-30