The U.S. Geological Survey compiled historical data about Old Faithful Geyser (Yellowstone National Park) from 1870 to 1987. Let x1 be a random variable that represents the time interval (in minutes) between Old Faithful eruptions for the years 1948 to 1952. Based on 9260 observations, the sample mean interval was x1 = 62.6 minutes. Let x2 be a random variable that represents the time interval in minutes between Old Faithful eruptions for the years 1983 to 1987. Based on 25,340 observations, the sample mean time interval was x2 = 70.6 minutes. Historical data suggest that σ1 = 8.14 minutes and σ2 = 12.97 minutes. Let μ1 be the population mean of x1 and let μ2 be the population mean of x2.
(a) Compute a 95% confidence interval for μ1 – μ2. (Use 2 decimal places.)
lower limit _________
upper limit _________
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