Midterm Examination #1
Sta 113: Probability and Statistics in Engineering
Tuesday, 2008 Sep. 23, 1:15 – 2:30 pm
This is a closedbook exam so do not refer to your notes, the text, or any
other books (please put them on the floor). You may use a single sheet of
notes or formulas and a calculator, but materials may not be shared.
A
formula sheet and two blank worksheets are attached to the exam.
You must show your work to get partial credit. Even correct answers will
not receive full credit without justification.
Please give all numerical answers to at least two correct digits
or as exact fractions reduced to lowest terms
. Write your solutions
as clearly as possible and make sure it’s easy to find your answers (circle
them if necessary), since you will not receive credit for work that I cannot
understand or find. Good Luck!
If you find a question confusing please
ask me
to clarify it.
Cheating on exams is a breach of trust with classmates and faculty, and will
not be tolerated. After completing the exam please acknowledge the Duke
Honor Code with your signature below:
I have neither given nor received unauthorized aid on this exam
.
Signature:
Print Name:
1.
/15
2.
/25
3.
/25
4.
/25
5.
/10
Total:
/100
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Name:
Sta 113
Problem 1:
Let
A, B, C
denote events in a probability space with
P
(
A
)
, P
(
B
)
, P
(
C
)
>
0. Decide if the following statements are true or false for any
A, B, C
and
explain WHY. (15 pts)
i.
P
(
A
∪
B
) =
P
(
A
)+
P
(
B
) implies that the events
A
and
B
are disjoint.
True. If
A
and
B
are disjoint then the above is true.
ii. If
A
and
B
are disjoint then
P
(
A
∩
B
) =
P
(
A
)
P
(
B
)
.
The above can be either True or False depending on the explanation.
If
A
and
B
are disjoint then the above can be true if either
P
(
A
) = 0
or
P
(
B
) = 0 since
P
(
A
∩
B
) = 0. If neither are zero then it is False.
iii. The variance of a hypergeometric distribution and the variance of the
binomial distribution are equal for a fixed
p, n
.
False. The variance of the hypergeometric is greater.
iv.
P
(
A

B
∩
C
)
>
P
(
A
∩
B
∩
C
)
P
(
B

C
)
P
(
C
)
.
False. The above is an equality.
P
(
A

B
∩
C
) =
P
(
A
∩
B
∩
C
)
P
(
B

C
)
P
(
C
)
.
v. The probability density function for a random variable is always bounded
between zero and one.
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 Fall '08
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 Statistics, Probability, Variance, Probability distribution, Probability theory, Democrats, ... ..., µ

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