STAT 200 Quiz 2

1. (10 points) Once upon a time, I had a fast-food lunch with a mathematician colleague. I
noticed a very strange behavior in him. I called it the Au-Burger Syndrome since it was
discovered by me at a burger joint. Based on my unscientific survey, it is a rare but real malady
inflicting 2% of mathematicians worldwide. Yours truly has recently discovered a screening test
for this rare malady, and the finding has just been reported to the International Association of
Insane Scientists (IAIS) for publication. Unfortunately, my esteemed colleagues who reviewed
my submitted draft discovered that the reliability of this screening test is only 80%. What it
means is that it gives a positive result, false positive, in 20% of the mathematicians tested even
though they are not afflicted by this horribly-embarrassing malady.
I have found an unsuspecting victim, oops, I mean subject, down the street. This good old
mathematician is tested positive! What is the probability that he is actually inflicted by this rare
disabling malady?
2. (5 points) Most of us love Luzon mangoes, but hate buying those that are picked too
early. Unfortunately, by waiting until the mangos are almost ripe to pick carries a risk of having
15% of the picked rot upon arrival at the packing facility. If the packing process is all done by
machines without human inspection to pick out any rotten mangos, what would be the
probability of having at most 2 rotten mangos packed in a box of 12?
3. (5 points) We have 7 boys and 3 girls in our church choir. There is an upcoming concert in
the local town hall. Unfortunately, we can only have 5 youths in this performance. This
performance team of 5 has to be picked randomly from the crew of 7 boys and 3 girls.
a. What is the probability that all 3 girls are picked in this team of 5?
b. What is the probability that none of the girls are picked in this team of 5?
c. What is the probability that 2 of the girls are picked in this team of 5?
4. (10 points) In this economically challenging time, yours truly, CEO of the Outrageous
Products Enterprise, would like to make extra money to support his frequent filet-mignon-anddouble-lobster-tail
dinner habit. A promising enterprise is to mass-produce tourmaline wedding
rings for brides. Based on my diligent research, I have found out that women’s ring size
normally distributed with a mean of 6.0, and a standard deviation of 1.0. I am going to order
5000 tourmaline wedding rings from my reliable Siberian source. They will manufacture ring
size from 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, and 9.5. How many wedding rings
should I order for each of the ring size should I order 5000 rings altogether? (Note: It is
natural to assume that if your ring size falls between two of the above standard manufacturing
size, you will take the bigger of the two.)
5. (5 points) A soda company want to stimulate sales in this economic climate by giving
customers a chance to win a small prize for ever bottle of soda they buy. There is a 20% chance
that a customer will find a picture of a dancing banana ( ) at the bottom of the cap upon
opening up a bottle of soda. The customer can then redeem that bottle cap with this picture for a
small prize. Now, if I buy a 6-pack of soda, what is the probability that I will win something,
i.e., at least winning a single small prize?
6. (5 points) When constructing a confidence interval for a population with a simple random
sample selected from a normally distributed population with unknown σ, the Student tdistribution
should be used. If the standard normal distribution is correctly used instead, how
would the confidence interval be affected?
7. (10 points) Below is a summary of the Quiz 1 for two sections of STAT 225 last spring. The
questions and possible maximum scores are different in these two sections. We notice that
Student A4 in Section A and Student B2 in Section B have the same numerical score.
Section A
Student Score
Section B
Student Score
A1 70 B1 15
A2 42 B2 61
A3 53 B3 48
A4 61 B4 90
A5 22 B5 85
A6 87 B6 73
A7 59 B7 48
—– —— B8 39
How do these two students stand relative to their own classes? And, hence, which student
performed better? Explain your answer.
8. (5 points) My brother wants to estimate the proportion of Canadians who own their house.
What sample size should be obtained if he wants the estimate to be within 0.02 with 90%
confidence if
a. he uses an estimate of 0.675 from the Canadian Census Bureau?
b. he does not use any prior estimates? But in solving this problem, you are actually using a
form of “prior” estimate in the formula used. In this case, what is your “actual” prior
estimate? Please explain.
9. (5 points) An amusement park is considering the construction of an artificial cave to attract
visitors. The proposed cave can only accommodate 36 visitors at one time. In order to give
everyone a realistic feeling of the cave experience, the entire length of the cave would be chosen
such that guests can barely stand upright for 98% of the all the visitors.
The mean height of American men is 70 inches with a standard deviation of 2.5 inches. An
amusement park consultant proposed a height of the cave based on the 36-guest-at-a-time
capacity. Construction will commence very soon.
The park CEO has a second thought at the last minute, and asks yours truly if the proposed
height is appropriate. What would be the proposed height of the amusement park
consultant? And do you think that it is a good recommendation? If not, what should be the
appropriate height? Why?
10. (5 points) A department store manager has decided that dress code is necessary for team
coherence. Team members are required to wear either blue shirts or red shirts. There are 9 men
and 7 women in the team. On a particular day, 5 men wore blue shirts and 4 other wore red
shirts, whereas 4 women wore blue shirts and 3 others wore red shirt. Apply the Addition Rule to
determine the probability of finding men or blue shirts in the team.
Please refer to the following information for Question 11 and 12.
It is an open secret that airlines overbook flights, but we have just learned that bookstores
underbook (I might have invented this new term.) textbooks in the good old days that we had to
purchase textbooks.
To make a long story short, once upon a time, our UMUC designated virtual bookstore, MBS
Direct, routinely, as a matter of business practice, orders less textbooks than the amount
requested by UMUC’s Registrar’s Office. That is what I have figured out……. Simply put, MBS
Direct has to “eat” the books if they are not sold. Do you want to eat the books? You may want
to cook the books before you eat them! Oops, I hope there is no account major in this class?
OK, let us cut to the chase….. MBS Direct believes that only 85% of our registered students
will stay registered in a class long enough to purchase the required textbook. Let’s pick on our
STAT 200 students. According to the Registrar’s Office, we have 600 students enrolled in STAT
200 this spring 2014.
11. (10 points) Suppose you are the CEO of MBS Direct, and you want to perform a probability
analysis. What would be the number of STAT 200 textbook bundles you would order so that
you stay below 5% probability of having to back-order from Pearson Custom Publishing? (Note:
Our Provost would be very angry when she hears that textbook bundles have to be backordered.
In any case, we no longer need the service of MBS Direct as we are moving to 100% to
free eResources. Auf Wiedersehen, MBS Direct……)
IMPORTANT: Yes, you may use technology for tacking Question 11 in this quiz.
12. (5 points) Is there an approximation method for Question 11? If so, please tackle Question
11 with the approximation method.

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