A work sampling study is to be performed on an office pool consisting of 10 persons to see how much time they spend on t

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A work sampling study is to be performed on an office pool
consisting of 10 persons to see how much time they spend on the
telephone. The duration of the study is to be 22 days, 7hr/day. All
calls are local. Using the phone is only one of the activities that
members of the pool accomplish. The supervisor estimates that 25%
of the workers’ time is spent on the phone. (a) At the 95%
confidence level, how many observations are required if the lower
and upper limits on the confidence interval are 0.20 and 0.30. (b)
Regardless of your answer to (a), assume that 200 observations were
taken on each of the 10 workers (2000 observations total), and
members of the office pool were using the telephone in 590 of these
observations. Construct a 95% confidence interval for the true
proportion of time on the telephone. (c) Phone records indicate
that 3894 phone calls (incoming and outgoing) were made during the
observation period. Estimate the average time per phone call.