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Given the sample mean, population standard deviation, and confidence level, use the one-mean z-interval procedure to find a confidence interval for the mean of the population.
X‾ =25 , n = 36 , σ = 3 , Confidence level = 95%

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James F. | Statistics Graduate Student and TutorStatistics Graduate Student and Tutor
5.0 5.0 (6 lesson ratings) (6)
When you want a 95% confidence interval for µ (population mean) and σ (population standard deviation) is known, we use the formula:
X-bar ± Z.975*σ/√n
X-bar is the sample average
Z.975 is the critical value for which if Z~Normal(0,1) then P(Z<Z.975) = .975.  This can be looked up on a Normal table.  Make sure you are able to use these tables, but Z.975 = 1.96.
σ is the population standard deviation
n is the sample size