MAT 2378
Midterm
practice
26 October, 2009
Professor: R. Kulik
Time: 70 minutes
Student Number:
Family Name:
First Name:
This is a closed book examination.
Only nonprogrammable and nongraphic calculators are permitted.
Record your answer to each question in the table below.
Number of pages: .
NOTE: At the end of the examination, hand in only this page. You may keep the questionnaire.
Question
Answer
1
2
3
4
5
6
7
8
9
10
1
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1
Q
1.
(2.23) As a part of a classic experiment on mutations, ten aliquots of identical size were taken from the same
culture of the bacterium
E.coli
.
For each aliquot, the number of bacteria resistant to a certain virus was
determined. The results were as follows:
14 15 13 21 14 14 26 16 20 13
The mean, median and the third quartile are, respectively, :
(a)
16.6; 14.5; 14
(b)
16.6; 14.5; 20
(c)
16.6; 14; 20
(d)
18.1; 14.5; 20
(e)
none of the preceding
Q
2.
Suppose a certain drug test is 99% sensitive and 99% specific, that is, the test will correctly identify a drug user
as testing positive 99% of the time, and will correctly identify a nonuser as testing negative 99% of the time.
Let’s assume a corporation decides to test its employees for opium use, and it is known 0.5% of the employees
use the drug. The probability that, given a positive drug test, an employee is actually a drug user, is:
HINT: compare Question 1 in Assignment 3.
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 Spring '09
 Kulik
 Probability, drug user

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