ECMT5001: In-semester Exam (2022s1)
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ECMT5001: In-semester Exam (2022s1)
1. [Total: 9 marks] Bob is the proud owner of the restaurant ìHungry Bob.î The only product Hungry Bob sells is Bobís burger, which is priced at $10 each. The number of Bobís burgers sold on a day, denoted N, follows a normal distribution with mean 400 and standard deviation 50.
(a) [3 marks] What is the probability that the daily revenue exceeds $5,000?
It is known that the total daily cost, denoted C, follows a normal distribution with mean $1,000 and standard deviation $300. The correlation between C and N is 0.8. Let P denote the total daily proÖt.
(b) [1 mark] Express P in terms of C and N .
(c) [2 marks] Compute E(P).
(d) [3 marks] Compute Var(P).
2. [Total: 16 marks] The government reported that the infection rate of COVID-19 is 0.2. Let Y denote the number of people infected with COVID-19 in a random sample of 5 individuals.
(a) [3 marks] What is the distribution of Y? Name the distribution and specify its
parameter(s).
(b) [3 marks] Compute P(Y > 1).
(c) [4 marks] Compute P(Y > 2|Y > 1).
(d) [6 marks] Simon wanted to test whether the true infection rate is higher than 0.2. He collected a random sample of 100 individuals. It was found that 27 individuals were infected with COVID-19. Carry out a hypothesis test for Simon at the 5 percent signiÖcance level. Show all your steps. A complete response should include:
i. setting up the null and alternative hypotheses;
ii. deÖning an appropriate test statistic;
iii. stating the distribution of your test statistic under the null hypothesis;
iv. computing the test statistic based on the sampled data;
v. making a decision using a correct method (e.g., critical value approach or p-value approach); and
vi. drawing a conclusion.
3. [Total: 15 marks] Carol is a trader for an investment bank in Wall Street. She is studying the tick movement of a blue chip stock. Let X denote the price change (in number of ticks). The probability density function of X is given below.
x |
f(x) |
-2 |
0.02 |
-1 |
0.08 |
0 |
0.8 |
1 |
0.08 |
2 |
0.02 |
(a) Compute the following:
i. [2 marks] E(X)
ii. [2 marks] E(X2)
iii. [2 marks] sd(X)
(b) Let S denote the sign of X, deÖned below
í _1
S = 0
( 1
if X is negative,
if X = 0,
if X is positive.
Let |X| denote the absolute value of X (e.g., |_2| = 2, |2| = 2). Note that |X| = SX and X = S |X|.
i. [3 marks] Compute Cor(S;|X|), the correlation between S and |X|.
ii. [4 marks] Compute Cor(S;X), the correlation between S and X .
iii. [2 marks] Are S and X independent? Why or why not?
2022-09-12