Econometrics Exam 0
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Sept. 5, 2008
your intention to abide by the honor pledge:
PID:
This exam consists of
ten
short questions
(
worth four points apiece
)
and
three
long
questions
(
worth twelve points each
)
, for a total of 76 points.
You have 50 minutes
to answer all completely and clearly in the space provided.
For better and for worse,
I am grading you primarily on technique and secondarily on correct answers.
Short Questions
1. Suppose that
X
has a mean of
5
, and variance of
9
;
Y
has a mean of
7
, and
variance of
16
; the two random variables are independent.
If you created
Z
=
2
X
!
Y
, what would be
E
[
Z
]
and
Var
(
Z
)
?
2. Given three matrices
A
,
B
, and
C
, rewrite the expression
(
A
+
BC
!
)
without
parentheses.
3.
What is the difference between “
Var
(
X
)
” and “
V
ˆ
ar
(
X
)
”?
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4.
Define the following matrices as:
y
=
y
1
y
2
!
"
#
$
%
&
A
=
2
!
3
3
6
"
#
$
%
&
’
x
=
x
1
x
2
!
"
#
$
%
&
If
y
=
Ax
, then what is
y
1
equal to
(
in terms of
x
1
and
x
2
)
?
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 Spring '08
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 Econometrics, Variance, 1%, Corr, 2 0, $0 3, 0 3

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