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 9440 observations, the sample mean interval was x1 = 63.6 minutes. Let x2 be a random variable that represents

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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 9440 observations, the sample mean interval was x1 = 63.6 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 24,053 observations, the sample mean time interval was x2 = 72.8 minutes. Historical data suggest that ?1 = 8.21 minutes and ?2 = 12.62 minutes. Let ?1 be the population mean of x1 and let ?2 be the population mean of x2.

(a) Compute a 95% confidence interval for ?1 – ?2. (Use 2 decimal places.)
lower limit     =__
upper limit     =__

 

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