College of Human Ecology
Cornell University
Ithaca, New York
Department of Policy Analysis and Management
PAM 2100 Intro Stats
A. Sinan
¨
Un¨ur – Fall 2008
Prelim 1 – Answer
October 2, 2008
Multiple Choice
MC 1)
Suppose you are told that the average score on the fall semester PAM 2100 prelim was 18
points and there were 50 students in the class. Then, you can be certain that
( a )
The number of students who scored lower than 18 points on the exam is equal to the
number of students who scored higher than
118 18 points.
( b )
The sum of all students’ scores is 900.
( c )
Most students scored 18 points on the exam.
( d )
The difference between the highest and lowest score is 10 points.
Answer
:
1b
.
∑
x
i
50
=
18
⇒
∑
x
i
=
900
.
MC 2)
For a research project involving human participants to be approved by the Institutional
Review Board at Cornell University, participants must
be able to withdraw from the
study without penalty.
( a )
never
( b )
occasionally
( c )
usually
( d )
always
Answer
:
2d
. There is no valid reason for forcing participants to stay in a study that might
make them uncomfortable or even harm them.
MC 3)
Consider data on the fuel efficiency of 40 car models. Suppose
Q
1
=
20 mpg and
Q
2
=
32
Q
3
=
32 mpg. Which one of the following statements is correct?
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MC 4)
According to the Census Bureau, the median earnings of male workers 25 and older in
the U.S. was $41,539 in 2007. In the same year, average earnings for the same group of
workers was $54,966. Based on this information, you can conclude that:
Answer
:
4a
. This is the correct answer among all the answers given (implicitly assumes
that the distribution is unimodal).
MC 5)
Assume that the speed at which people drive on I81 is normally distributed. Suppose you
are pulled over while driving at 80 mph on I81. The state trooper tells you the while the
average driver obeys the speed limit of 65 mph, 16% drive faster than you.
What is the
approximate standard deviation of the distribution of speeds at which people
drive on I81?
Answer
:
5c
Looking at the normal distribution, we note that a zscore of approximately 1
corresponds to a right tail probability of 16%. Therefore, we have
80

65
s
≈
1
.
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 Spring '10
 lewis
 Normal Distribution, Standard Deviation, median earnings level

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