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Confidence Interval for a Population Mean (t-interval)

x̄ ± t* · (s/√n). Use t* from t-table with df = n−1. Conditions: SRS, normality (n≥30 or nearly normal population).

StatisticsCommon Core UNC-4.BINFVerified correct ✓

Worked examples

A random sample of n = 50 observations gives x̄ = 95 and s = 15. Construct a 90% confidence interval for the population mean μ using t* = 1.677 (df = 49). What is the upper bound?
Answer: 98.5575
A random sample of n = 25 observations gives x̄ = 125 and s = 15. Construct a 90% confidence interval for the population mean μ using t* = 1.711 (df = 24). What is the upper bound?
Answer: 130.133

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