A store emails all of its (several thousands of) customers an online survey. Of all its customers, 302 reply to the survey and of these, 215 gave a five-star rating to their experience shopping at the store. The manager could estimate that 215/302 (or about 71%) of all customers would give a five-star rating, but why is a Z-interval not valid for a confidence interval here? Select all that apply. The proportion of the population of all customers is not approximately normal. The number of customers in the sample is not large enough. The sample was not randomly selected. The proportion of the population of all customers is known already.

An annual marathon covers a route that has a distance of approximately 26 miles. winning times for this marathon are all over 2 hours. the following data are the minutes over 2 hours for the winning male runners over two periods of 20 years each. earlier period 14 12 15 22 13 10 19 13 9 14 20 18 16 20 23 12 18 17 6 13 recent period 7 11 7 14 8 9 11 14 8 7 9 8 7 9 9 9 9 8 10 8 (a) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the earlier period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks. for more details, view how to split a stem.) minutes beyond 2 hours earlier period 0 1 2 (b) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the recent period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks.) minutes beyond 2 hours recent period (c) compare the two distributions. how many times under 15 minutes are in each distribution