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# Statistics - Confidence Interval

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1. The security department of a university is planning its budget for the next year. in estimating the man-hours for security during university sponsored music concerts, the average length of music concerts is needed. A random sample from 36 security depts. at universitites was taken and the sample mean length of concerts was 160 minutes. Suppose the population standard deviation is 45 minutes. A 95% confidence interval for the true mean duration of music concerts is?

2. You are interested in determining the average cost of a 3 minute phone call to locations in the US. what sample size must you take to be 96% confident that the results will be within \$.75 of the true mean cost per call? From the phone company you have gotten an estimate of o = 7.71

https://brainmass.com/statistics/confidence-interval/statistics-confidence-intervals-standard-deviation-222833

#### Solution Preview

(1) m = 160, n = 35, s = 45

SE = s/sqrt n = 45/sqrt 36 = 7.5

The 95% CI is given by [m - ...

#### Solution Summary

This solution helps with question about population standard deviation. Complete, Neat and Step-by-step Solutions are provided.

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