Suppose the amount of propane used per customer in a month is normally distributed with
. Find a 95 confidence interval for
if a randomly chosen sample of 30 customers has a mean propane usage of 110 gallons a month.
a.(78.6, 141.4)
b.(105.2, 114.8)
c.(103.2, 116.8)
d.(104.3, 115.7)
Question 2 Which of the following is
not a correct statement with regards to estimating a mean
using a known
?
a.If the sampling distribution for sample means
has a mean equal to
and a standard error equal to
and the randomly sampled population is normally distributed, then the sampling distribution of
has a normal distribution.
b.The sampling distribution of
is normally distributed only if the sampled population is normally distributed.
c.A necessary assumption for estimating a mean
using a known
is that the sampling distribution of
is normally distributed.
d.If the sampling distribution for sample means
has a mean equal to
and a standard error equal to
and the randomly sampled population is not normally distributed, then the sampling distribution of
is approximately normally distributed only for sufficiently large sample sizes.
Step 8 is very important. Be sure that the customer’s concern has been corrected.
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