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Answers to Quiz #2 for Econ 10a
1.
Since the sun must rise tomorrow, then the probability of
the sun rising tomorrow is
a.
much larger than one
b.
zero
c.
infinity
d.
None of these alternatives is correct.
Answer: d
2.
Which of the following statements is(are) always
true?
a. -1 £
P(Ei) £1
b.
P(A) = 1 - P(Ac)
c.
P(A) + P(B) = 1
d.
åP
³
1
Answer:
b
3.
If A and B are independent events with P(A) = 0.2 and P(B) = 0.6,
then
P(A U
B) =
a.
0.62
b.
0.12
c.
0.60
d.
0.68
Answer:
d
4.
If P(A) = 0.38, P(B) = 0.83, and P(A I
B) = 0.57; then P(A U
B) =
a.
1.21
b.
0.64
c.
0.78
d.
1.78
Answer:
b
5.
Which of the following is a required condition for a discrete
probability function?
a. Sf(x)
= 0
b. f(x) ³
1 for all values of x
c. f(x) < 0
d.
Sf(x)
= 1
Answer: d
6.
Assume that you have a binomial experiment with p = 0.5 and a
sample size of 100. The
expected value of this distribution is
a.
0.50
b.
0.30
c. 100
d.
50
Answer:
d
7. Forty percent of all
registered voters in a national election are female.
A random sample of 5 voters is selected. The probability that the
sample contains 2 female voters is
a.
0.0778
b.
0.7780
c.
0.5000
d.
0.3456
Answer:
d
8.
The expected value of a random variable is
a. the value of
the random variable that should be observed on the next repeat of the
experiment
b. the value of
the random variable that occurs most frequently
c. the square
root of the variance
d.
None of these alternatives is correct.
Answer:
d
9.
The variance for the binomial probability distribution is
a.
var(x) = P(1 - P)
b.
var(x) = nP
c.
var(x) = n(1 - P)
d.
var(x) = nP(1 - P)
Answer:
d
10.
Twenty percent of the students in a class of 100 are planning to
go to graduate school. The
standard deviation of this binomial distribution is
a. 20
b. 16
c. 4
d.
2
Answer:
c
11.
For any continuous random variable, the probability that the
random variable takes on exactly a specific value is
a.
1.00
b.
0.50
c. any value
between 0 to 1
d.
almost zero
Answer:
d
12.
Which of the following is not
a characteristic of the normal probability distribution?
a.
symmetry
b. The total
area under the curve is always equal to 1.
c. 99.72%
of the time the random variable assumes a value within plus or minus 1
standard deviation of its mean
d.
The mean is equal to the median, which is also equal to the mode.
Answer:
c
13.
Given that Z is a standard normal random variable, what is the
probability that
Z ³
-2.12?
a. 0.4830
b. 0.9830
c. 0.017
d.
0.966
Answer: b
14.
For a standard normal distribution, the probability of obtaining
a z value between
-1.9 to 1.7 is
a. 0.9267
b. 0.4267
c. 1.4267
d.
0.5000
Answer: a
15.
The point estimator with the smaller variance is said to have
a.
smaller relative efficiency
b.
greater relative efficiency
c.
smaller relative consistency
b.
greater relative consistency
Answer:
b
16.
As the sample size becomes larger, the sampling distribution of
the sample mean approaches a
a.
binomial distribution
b.
Poisson distribution
c.
normal distribution
c.
chi-square distribution
Answer:
c
17.
A property of a point estimator that occurs whenever the expected
value of the point estimator is equal to the population parameter it
estimates is known as
a.
consistency
b. the expected
value
c. the estimator
d.
unbiasedness
Answer:
d
18.
If σ is the standard deviation of a population of infinite
size, the standard error of a sample mean is always equal to:
a. s
b.
sample deviation
c. σ / sqrt
(n)
e.
population mean
Answer:
c
19.
The following information was collected from a simple random
sample of a population.
16
19
18
17
20
18
The point estimate of the population standard deviation is
a.
2.000
b.
1.291
c.
1.414
d.
1.667
Answer:
c
20.
The purpose of statistical inference is to provide information
about the
a.
sample based upon information contained in the population
b.
population based upon information contained in the sample
c.
population based upon information contained in the population
d.
mean of the sample based upon the mean of the population
Answer:
b
21.
Random samples of size 36 are taken from an infinite population
whose mean and standard deviation are 20 and 15, respectively. The distribution of the population is unknown.
The mean and the standard error of the mean are
a. 36 and 15
b. 20 and 15
c. 20 and 0.417
d.
20 and 2.5
Answer:
d
22.
F is a cumulative distribution function (CDF), which of the
followings is not correct?
a.
F(min) = 0
b.
F(median) = 0.50
c.
F(Q2) = 0.25
d.
F(max) = 1
Answer: c
23.
A local bank has determined that the daily balances of the
checking accounts of its customers are normally distributed with an
average of $280 and a standard deviation of $20. What percentage of its
customers has daily balances of more than $275?
Answers: 59.87%
24.
Assume two events A and B are mutually exclusive and,
furthermore, P(A) = 0.2 and P(B) = 0.4. Find P(AôB).
Answers: 0
25. Four
workers at a fast food restaurant pack the take-out chicken dinners. John packs 45% of the dinners but fails to include a salt
packet 4% of the time. Mary
packs 25% of the dinners but omits the salt 2% of the time.
Sue packs 30% of the dinners but fails to include the salt 3% of
the time. You have
purchased a dinner and there is no salt. Find the probability that Mary
packed your dinner.
Answers: 0.15625
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