SECTION I:
Multiple Choice [10 Marks]
Notes:
For each multiplechoice question below, select only ONE answer.
Write your answer in your ANSWER BOOKLET (not this question sheet)
[1 Mark Per Question]
1.
For a discrete random variable,
X
, which of the following statements is not true?
a)
We can evaluate all moments of
X
solely based on the probability mass function
b)
The standard deviation of
X
has the same units as the mean
c)
All moments of
X
are nonnegative
d)
The conditional mean and variance of
X
(conditioned on some event A) are examples of moments.
e)
Trellis diagrams, which represent the decoder of a Trellis Coded Modulation communication
system, implement successive products of conditional probabilities.
2.
Which of the following statements about conditional probability is not true?
a)
Conditioning always increases the probability of an event
b)
Conditioning may increase or decrease the probability of an event
c)
Conditioning changes the effective sample space of the experiment
d)
The Total Theorem of Probability allows one to compute unconditional probabilities by
combining conditional probabilities
3.
Assume that we select balls from an urn, at random.
From the following selection methods, which
method does not lead to equallyprobable events?
a)
With replacement with ordering
b)
Without replacement with ordering
c)
With replacement without ordering
d)
Without replacement without ordering
4.
If two events have nonzero probabilities and are mutually exclusive, then they:
a)
Must be independent
b)
Cannot be independent
c)
Can be independent or not independent
d)
Always form a partition
e)
Can never form a partition
5.
In a sequential experiment, if the outcome of the nth subexperiment s
n
depends only on that of the
(n1)th subexperiment s
n1
, which of the following statements is not true?
a)
It is a dependent sequential experiment
b)
c)
s
n
and s
n2
are independent
d)
For a given s
n1,
s
n
and s
n2
are independent
e)
None of the above (i.e., they are all true)
6.
Which of the following statements about equivalent events is not true?
0
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 Spring '11
 Prof.ShenghuiSong

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