Question

A local telephone company claims that the average length of a phone call is 8 minutes in a random sample of 18 calls. The sample mean was 7.8 minutes and sample standard deviation was 0.5 minutes. Is there enough evidence to support the company’s claim at α=0.05.

Answer #1

1. A cigarette manufacturer claims that one-eighth of the US
adult population smokes cigarettes. In a random sample of 100
adults, 5 are cigarette smokers. Test the manufacturer's claim at
alpha= 0.05. (critical values of z are ±
1.96).
2. A local telephone company claims that the average length of a
phone call is 8 minutes. In a random sample of 58 phone calls, the
sample mean was 7.8 minutes and the standard deviation was 0.5
minutes. Is there enough evidence...

About 10,000 employees of the Internal Revenue Service were
brought back to 10 offices last Monday. The IRS claims that the
standard deviation of the lengths of time it takes an incoming
phone call to be transferred to the correct office is less than 10
minutes. A random sample of 25 incoming phone calls has a standard
deviation of 9 minutes. At α = 0.1, is there enough evidence to
support the IRS’s claim?

A call center claims their average call lasts 6 minutes. Let's
take a sample of 30 call center agents with a mean of 7.2 minutes
and a standard deviation of 1.9 minutes. Can the claim at an alpha
of 0.08?

33. A researcher claims that the average wind speed in a certain
city is 8 miles per hour. In a random sample of 32 days, the
average wind speed is 8.2 miles per hour. The standard deviation of
the sample is 0.6 miles per hour. At α = 0.05 is there enough
evidence to reject the claim?

From her firm's computer telephone log, an executive found that
the mean length of 70 telephone calls during July was 4.19 minutes
with a standard deviation of 5.46 minutes. She vowed to make an
effort to reduce the length of calls. The August phone log showed
50 telephone calls whose mean was 2.134 minutes with a standard
deviation of 2.752 minutes.
Steps:
1. Open Minitab on your computer.
2. There is no data file for this example. The
information above...

A state executive claims that the average cost of tuition at
public colleges is $5700. A researcher wishes to test the claim
that this cost is greater than $5700. She selects a random sample
of 36 public colleges and finds the mean to be $5950.The population
standard deviation is $659. Is there enough evidence to support the
claim that the cost of tuition is greater than $5700 at α = 0.05
?

40. A cell phone manufacturer claims that its phone will last
for more than 8 hours of continuous talk time when the battery is
fully charged. To test this claim at a 10% level of significance,
a random sample of 18 phones were selected. The results showed a
sample mean of 8.2 hours and a sample standard deviation of 0.4
hour.
Based on the data and hypothesis test, can you dispute the cell
phone manufacturer’s claim?
A.
YES
B.
NO...

A movie critic claims the mean run time for movies in theaters
is 100 minutes. Researchers are trying to prove that the mean run
time is actually longer than that though (Ha : µ > 100). In a
random sample of 16 movies, the mean run time was found to be 105
minutes with a sample standard deviation of 12 minutes. Assume the
population is normally distributed. At α = 0.05, is there enough
evidence to reject the movie critic’s...

The length of mobile phone calls for teenagers is known to be
normally distributed, with a mean calling time of 5 minutes and a
standard deviation of 1.5 minutes. If a random sample of 36 phone
calls is selected, what is the probability that the sample average
time spent on calls is between 4.25 minutes and 5.75 minutes (four
decimal places)?

A local pizza place claims that they average a delivery time of
7.32 minutes. To test this claim, you order 11 pizzas over the next
month at random times on random days of the week. You calculate the
average delivery time and sample standard deviation from the 11
delivery times (minutes), and with the sample mean and sample
standard deviation of the time (minutes), you create a 95%
confidence interval of (7.648, 9.992). (delivery time is normally
distributed)
a. What...

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