STATS 2103: Probability and Statistics II: Assignment 5
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STATS 2103: Probability and Statistics II: Assignment 5
Semester 1 2023
CHECKLIST
• □ : Have you shown all of your working, including probability notation where necessary?
• □ : Have you given all numbers to 3 decimal places unless otherwise stated?
• □ : Have you made sure that all plots and tables each have a caption?
• □ : If before the deadline, have you submitted your assignment via the online submission on Canvas?
• □ : Is your submission a single pdf file - correctly orientated, easy to read? If not, penalties apply.
• □ : Penalties for more than one document - 10% of final mark for each extra document. Note that you
may resubmit and your final version is marked, but the final document should be a single file.
• □ : The assignment is due at 5:00 pm Friday, not 5:00 pm Saturday. The extra 24 hours submission
time in the system is only a “buffer’’for technical issues when submitting your assignment. Extensions
will not be considered after 5:00 pm Friday.
• □: Assignments emailed instead of submitted by the online submission on Canvas will not be marked
and will receive zero.
• □ : Have you checked that the assignment submitted is the correct one, as we cannot accept other
submissions after the due date?
Due date: Friday 26th May 2023 (Week 11), 5pm.
Q1: Covariance of normals. Let Z be a standard normal random variable and let Y1 = Z and Y2 = Z2 .
a. What are E[Y1] and E[Y2]? [3 marks]
b. What is E[Y1 Y2]? Hint: use the MGF. [3 marks]
c. What is cov(Y1 , Y2 )?
[2 marks] [Question total: 8]
Q2: Beta-binomial Suppose that Y has a binomial distribution with parameters n and P , but that P varies from day to day according to a beta distribution with parameters α and β . Show that
a. E[Y] =
[4 marks]
b. var(Y) = (α(n)β(β))1)
You may use the expectated value and variance of the beta distribution without deriving them:
https://en.wikipedia.org/wiki/Beta_distribution
[5 marks] [Question total: 9]
Q3: Vending machine A vending machine can be in two states, (0=working, 1=out of order). If the machine is working on a particular day it will be out of order with probability 6 on the next day. If the machine is out of order on a particular day then the probability that it will be working the next day is γ .
a. Write down the one step transition probability matrix for the vending machine. [4 marks]
b. Assume the machine is working on Monday. What is the probability that the machine will remain working on all of Tuesday, Wednesday and Thursday? [2 marks]
c. Assume the machine is working on Monday. What is the probability that the machine will be working on Thursday? [4 marks]
d. Calculate the equilibrium probabilities for the states of the vending machine.
[5 marks] [Question total: 15] [[Assignment total: 32]]
2023-05-28