16. Suppose we know Bob went on a long trip. What is the chance that he forgot to pack
something important?
a.
0.60
b.
0.80
c.
0.75
d.
None of the above
17.
Whether or not Bob forgot something important is INDEPENDENT of length of his
trip.
18.
What can we tell from the probabilities in the above table?
a.
Bob forgets something important just as often
when he takes a short trip compared to a
long trip.
b.
Bob forgets something important more often
when he takes a short trip compared to a
long trip.
c.
Bob forgets something important less as often
when he’s on a short trip as he does on a
long trip.
19. The mean of a random variable X can never be negative.
20. Suppose the standard deviation of X equals 4. Then the standard deviation of 2X is equal to
which of the following?
a.2
b.
4
c.8
d.
16
21. If two events are independent, what is the probability that they both occur?
22.
Which of the following is not
true about a continuous random variable?
a.
The probability of a single value of X is 0.
b.
Probabilities are found by finding areas under a curve over specified intervals.
c.
Values of the density function, f(x), must always be between 0 and 1, for all x.
d.
All of the above statements are true about a continuous random variable.
23. If A and B are disjoint events where P(A) = 0.20 and P(B) = 0.30, then P(A and B) equals:
5
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24. If P(A) = 0.84, P(B) =0.76 and P(A or B) =0.90, then P(A and B) is:
Problems 2526. Suppose 63% of the U.S. population is annoyed by other people’s cell
phone conversations. Of those who are annoyed, only 32% have cell phones. Of those not
annoyed, 51% own cell phones.
25. What is the chance that a person in the U.S. has a cell phone?
a.83%
b.
39%
c.32%
d.
16%
26. Choose 10 people from the U.S. at random. What is the chance that at least one of
them is annoyed by other people’s cell phone conversations?
27. It is possible for a relationship that you found between two variables to actually
reverse direction if you add a third confounding variable to the mix.
a.TRUE
b. FALSE
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 Winter '12
 Johnson
 Statistics, Standard Deviation, Probability theory, A.

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