Practice Midterm 2
A producer of household products uses an automated process to fill containers with chlorine bleach. When
the process is in control, the population mean amount of bleach in the containers is μ=128 ounces with
standard deviation σ=1.6 ounces. Each hour, a technician selects a random sample of 16 filled containers
and computes the average amount in the containers.
__B__1. The concept of “sampling variation” tells us that we should expect which of the following:
(a)
The population mean will be different each time a sample is selected.
(b)
The average amount in the containers will vary from sample to sample even if the process remains in
control.
(c)
The average amount in the containers will vary from sample to sample only if the population mean
amount is not equal to 128 ounces.
(d)
The average amount in the containers computed each hour will be equal to 128 ounces as long as the
process remains in control.
(e)
A larger sample selected each hour for the computation of the average amount will eliminate any
variation in the average amounts when the process is in control.
A contractor involved in highrise building construction orders thousands of steel rods each year from a
supplier. The strength, X, of the rods is a normally distributed random variable. When a shipment arrives,
the contractor selects a random sample of 15 rods and determines the sample mean strength and the sample
standard deviation. These results are then used to compute a confidence interval for the population mean
strength of the rods.
__C__2. For a particular shipment, the sample mean strength of the selected rods is 990 pounds and the
sample standard deviation is 14.5 pounds. What is the margin of error for a 95% confidence interval for the
population mean strength? (Round your answer to2 decimal places.)
(a) 7.98 pounds
(b) 2.07 lbs.
(c) 8.03 lbs.
(d) 7.34 lbs.
(e) 8.31 lbs.
__C__3. The contractor would like to have an interval that has a smaller margin of error than the one in #4.
Which of the following would contribute to accomplishing this goal? (Choose the most appropriate
response.)
(a)
Increase the level of confidence to 99%.
(b)
Decrease the size of the sample mean strength.
(c)
Increase the size of the sample to 30 rods.
(d)
Increase the population mean strength.
(e)
Both (b) and (c) would contribute to a reduction in the margin of error.
A manufacturer of flu medicine claims in its advertising that “90% of people with the flu get relief from
their symptoms” when using this medicine. A consumer group selects a random sample of 400 people
suffering from flu symptoms and provides them with this medicine.
After using the medicine, 348 of the
people indicate that they did get relief from the flu symptoms.
__D__4. Determine a 98% confidence interval for the population proportion of people with the flu who will
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 Spring '07
 Lv
 Standard Deviation, Statistical hypothesis testing

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