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1) If the time it takes for a customer to be served at a fastfood chain business is thought to be
uniformly distributed between 3 and 8 minutes, what is the probability that the time it takes
for a randomly selected customer will be less than 5 minutes?
A) 0.30
B) 0.80
C) 0.40
D) 0.20
2) The manager of a computer help desk operation has collected enough data to conclude that
the distribution of time per call is normally distributed with a mean equal to 8.21 minutes and
a standard deviation of 2.14 minutes.
The manager has decided to have a signal system
attached to the phone so that after a certain period of time, a sound will occur on her
employees' phone if she exceeds the time limit.
The manager wants to set the time limit at a
level such that it will sound on only 8 percent of all calls.
Let P(Z < 1.41) = 0.92, P(Z <
1.41) = 0.08, the time limit should be:
A) approximately 5.19 minutes
B) about 14.58 minutes.
C) 10.35 minutes.
D) about 11.23 minutes.
3) The monthly electrical utility bills of all customers for the Far East Power and Light
Company are known to be distributed as a normal distribution with mean equal to $87 a
month and standard deviation of $36.
If a statistical sample of n = 100 customers is selected
at random, what is the probability that the mean bill for those sampled will exceed $75? Let
P(Z < 3.33) = 0, P(Z < 0.33) = 0.63 and P(Z < 0.44) = 0.33.
A) 0.33
B) Approximately 0.63
C) About 1.00 D) None of the others.
4) In an application to estimate the mean number of miles that downtown employees
commute to work roundtrip each day, the following information is given: n = 20;
= 4.33; s =
3.50. The point estimate for the true population mean is:
A). 1.638.
B) 4.33
C) 4.33 ± 1.638.
D) None of the above.
5) A major tire manufacturer wishes to estimate the mean tread life in miles for one of their
tires. They wish to develop a confidence interval estimate that would have a maximum
sampling error of 500 miles with 90 percent confidence. Let population standard deviation
equal to 4,000 miles.
Based on this information and let z
0.05
= 1.645, the required sample size
is:
A) 196.
B) 124.
C) 246.
D) 174.
6) Given
= 15.3, s = 4.7, and n = 18, form a 99% confidence interval for σ
2
. Let
A) (13.61, 43.30)
B) (10.51, 65.88)
C) (2.24, 14.02)
D) (11.13, 69.79)
7) In an application to estimate the mean number of miles that downtown employees
commute to work roundtrip each day, the following information is given: n = 20;
= 4.33; s =
3.50. Based on this information and let t
0.025,19
= 2.09, the upper limit for a 95 percent
confidence interval estimate for the true population mean is:
A) about 5.97 miles.
B) nearly 12.0 miles.
C) about 7.83 miles.
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 Probability

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