# HOMEWORK 4 – STAT 3360 – FALL 2015

August 30, 2017

Question
HOMEWORK 4 – STAT 3360 – FALL 2015
DUE BY SEPTEMBER 29
PLEASE, SUBMIT THIS DOCUMENT AND SHOW YOUR FIRST AND LAST NAME BELOW!
1
SECTION [CIRCLE ONE! =>] 001 002 501
FIRST NAME LAST NAME
PROBLEM 1 [30 POINTS = 5 + 10 + 15]
THE NUMBER (X) OF CARS SOLD BY A RANDOMLY SELECTED DEALERSHIP IN THE
METROPLEX AREA DURING ONE DAY HAS A DISTRIBUTION SHOWN BELOW.
X = NUMBER OF CARS SOLD PROBABILITY
2 0.15
3 0.30
4 0.25
5 0.20
6 0.10
1. DETERMINE THE EXPECTED VALUE OF X.
E [X] =
2. WHAT IS THE VARIANCE OF X?
VAR [X] =
3. THE COMMISSION IS DEFINED (IN \$1,000) AS Y = 16 + 5 X.
FIND THE EXPECTATION AND VARIANCE OF Y.
E [Y] =
VAR [Y] =

2
PROBLEM 2 [20 POINTS = 5 + 5 + 5 + 5]
TWO RANDOM VARIABLES, X AND Y, ARE INDEPENDENT. THEIR MARGINAL
DISTRIBUTIONS ARE SPECIFIED AS FOLLOWS.
X – 10 0 5
PROBABILITY 10% 40% 50%
Y – 4 6
PROBABILITY 70% 30%
1. FIND EXPECTATION FOR EACH VARIABLE.
E [X] =
E [Y] =
2. FIND THE VARIANCE FOR EACH VARIABLE.
VAR [X] =
VAR [Y] =
3. WHAT IS THE EXPECTATION OF THE NEW RANDOM VARIABLE, Z = 3X – 2Y?
E [Z] =
4. FIND THE VARIANCE OF Z (= 3X – 2Y).
VAR [Z] =

3
PROBLEM 3 [50 POINTS = 10+15+15+10]
SUZY IS A STOCK MARKET ANALYST. SHE WANTS TO BUILD A PORTFOLIO INVESTING
50% INTO ONE STOCK AND 50% INTO THE OTHER. THREE STOCKS (I, II, AND III) ARE
CONSIDERED FOR SELECTION. THEIR EXPECTED ROI VALUES (IN CENTS PER DOLLAR)
AND CORRESPONDING STANDARD DEVIATIONS (IN CENTS PER DOLLAR) ARE LISTED IN
THE TABLE BELOW.
STOCK ROI EXPECTED ROI STANDARD DEVIATION
I X 14 5
II Y 14 5
III Z 14 5
IN ADDITION, SUZY ASSUMES THAT THE CORRELATION BETWEEN THE ROI FOR STOCK I
AND THAT FOR STOCK II IS C [X, Y] = – 0.8, WHILE THE ROI FOR STOCK III IS
UNCORRELATED WITH THAT FOR STOCK I (THAT IS C [Z, X] = 0). CORRELATION
BETWEEN THE ROI FOR STOCK II AND THAT FOR STOCK III WAS SET AS C [Y, Z] = 0.6.
SHE WANTS TO MAKE A CHOICE BETWEEN TWO TYPES OF SCENARIO.
FIRST SCENARIO OPERATES WITH STOCKS I AND II, SO THE ROI FOR THE PORTFOLIO
WILL BE FOUND AS T = 0.5 X + 0.5 Y.
THE ALTERNATIVE SCENARIO WILL OPERATE WITH STOCKS II AND III, SO THE ROI IN
THIS CASE WILL BE W = 0.5 Y + 0.5 Z.
HELP SUZY COMPARE TWO CHOICES FOR THE PORTFOLIO BY ANSWERING THE
FOLLOWING QUESTIONS.
1. WHAT IS THE EXPECTED ROI FOR T AND THAT FOR W?
E [T] =
E [W] =
2. WHAT IS THE VOLATILITY (STANDARD DEVIATION) ASSOCIATED WITH THE
PORTFOLIO CHARACTERIZED BY A RANDOM VARIABLE T?
SD [T] =
3. WHAT IS THE VOLATILITY (STANDARD DEVIATION) ASSOCIATED WITH THE
PORTFOLIO CHARACTERIZED BY A RANDOM VARIABLE W?
SD [W] =
4. BASED ON VOLATILITY COMPARISON, WHICH SCENARIO (T OR W) WOULD YOU
RECOMMEND?

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