The National Bank of Hamilton has opened up two new drive-through teller windows outside its main office building in downtown Hamilton. The bank is not sure that it needs both windows open all day so it has decided to conduct a work sampling study to determine the proportion of time the two tellers are idle between the hours of 10:00 A.M. to 11:30 A.M. and 1:00 P.M. to 3:00 P.M. The work sampling study was conducted at random over a five-day period, and the following observations were recorded:

a. Bank management wants the study to be ±5% accurate with a 95% confidence level. How many additional sample observations should be taken?
b. If the bank does not want to conduct a study of more than 100 observations, what level of confidence could itexpect?

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