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Mean Sampling Distributions
Statistics
Name______________________________
1) Taxi fares are normally distributed with mean fare $22.27 and standard deviation $2.20.
a) Which should have the greater probability of falling between $21 and $24 – the mean of 10 random taxi
fares or the amount of a single random taxi fare? Why?
b) Which should have a greater probability of being greater than $24 – the mean of 10 random taxi fares or
the amount of a single taxi fare? Why?
2) Suppose a sample of n = 50 items is drawn from a population of manufactured products and the weight, x,
of each item is recorded. Prior experience has shown that the weight has a mean of 6 ounces and standard
deviation of 2.5 ounces.
a) What is the shape of the sampling distribution of x ?
b) What is the mean and standard deviation of the sampling distribution?
c) What is the probability that the manufacturer’s sample has a mean weight of less than 5 ounces? If you
did get a sample mean of 5 or less, does this indicate that the manufacturing process may be faulty? Explain.
d) How would the sampling distribution of x change if the sample size, n, were increased from 50 to 100?
3) A soft-drink bottle vendor claims that its production process yields bottles with a mean internal strength of
157 psi (pounds per square inch) and a standard deviation of 3 psi and is normally distributed. As part of its
vendor surveillance, a bottler strikes an agreement with the vendor that permits the bottler to sample from the
vendor’s production to verify the vendor’s claim.
a) Suppose the bottler randomly selects a single bottle to sample. What is the mean and standard deviation?
b) What is the probability that the psi of the single bottle is 1.3 psi or more below the process mean?
c) Suppose the bottler randomly selected 40 bottles from the last 10,000 produced. Describe the sampling
distribution of the sample means?
d) What is the probability that the sample mean of the 40 bottles is 1.3 psi or more below the process mean?
e) In order to reduce the standard deviation 50% (half), how large would the sample size need to be?
4) In the library on a university campus, there is a sign in the elevator that indicates a limit of 16 persons.
Furthermore, there is a weight limit of 2500 pounds. Assume that the average weight of students, faculty,
and staff on campus is 150 pounds, that the standard deviation is 27 pounds, and that the distribution of
weights of individuals on campus is approximately normal. If a random sample of 16 persons from the
campus is to be taken:
a) What is the expected value of the sample mean of their weights?
b) What is the standard deviation of the sampling distribution of the sample mean weight?
c) What average weights for a sample of 16 people will result in the total weight exceeding 2500 pounds?
d) What is the probability that a random sample of 16 persons on the elevator will exceed the weight limit?