Question

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19. Length of Calls to the IRS. According to the IRS, taxpayers calling the IRS in 2017
waited 13 minutes on average for an IRS telephone assister to answer. Do callers
who use the IRS help line early in the day have a shorter wait? Suppose a sample
of 50 callers who placed their calls to the IRS in the first 30 minutes that the line is
open during the day have a mean waiting time of 11 minutes before an IRS telephone
assister answers. Based on data from past years, you decide that it is reasonable to
assume that the standard deviation of waiting times is 8 minutes. Using these sample
results, can you conclude that the waiting time for calls placed during the first 30
minutes the IRS help line is open each day is significantly less that the overall mean
waiting time of 13 minutes? Use a = .05.

19, 3 Mo = 13min
Ho M», 13 min
Ha M< 13 min
2= 0,05 min
n=50
o = 8 min
Z=1.645
11-13
13.
4.1645
--");
8/550 =177
-1.11 <1,645
- reject Ho M3 3
- We have 95% confidence that the first 30 minutes
the IRS help line is open
each day is significantly
less than 3 minutes