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)...

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 9800 observations, the sample mean interval was x1 = 61.6 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 24,638 observations, the sample mean time interval was x2 = 72.0 minutes. Historical data suggest that σ1 = 8.56 minutes and σ2 = 12.83 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.)

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