7. (a) [5 points] An accounting firm annually monitors the U.S. Postal Service (USP
of interest is the percentage of mail delivered on time. In a sample of 10,000 items mailed between Dec.
10 and Mar. 3-the most difficult delivery season due to
bad weather and holidays-the accounting firm
determined that 7,000 items were delivered on
time. Use this information to make a statement about
the likelihood of an item being delivered on time by the USPS. Assuming a
confidence level of 95%, the
confidence interval (CI) for the likelihood (in decimal form, rather
than %) of an item being delivered on
time (when it was mailed between Dec. 10 and Mar. 3) is (round to
three decimal places)
(i) (0.698, 0.702)
(ii) (0.599, 0.801)
(iii) (0.685, 0.715)
(iv) (0.691, 0.709)
(b) [5 points] Explain what is meant by the statement, "We are 95% confident that an interval estimate
contains ." (Note: there are many acceptable answers.)