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 9320 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 25,691 observations, the sample mean time interval was x2 = 73.0 minutes. Historical data suggest that σ1 = 8.70 minutes and σ2 = 11.64 minutes. Let μ1 be the population mean of x1 and let μ2 be the population mean of x2. (a) Compute a 90% confidence interval for μ1 – μ2. (Use 2 decimal places.) lower limit       upper limit

Holt Mcdougal Larson Pre-algebra: Student Edition 2012
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ISBN:9780547587776
Author:HOLT MCDOUGAL
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Chapter11: Data Analysis And Probability
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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 9320 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 25,691 observations, the sample mean time interval was x2 = 73.0 minutes. Historical data suggest that σ1 = 8.70 minutes and σ2 = 11.64 minutes. Let μ1 be the population mean of x1 and let μ2 be the population mean of x2.

(a) Compute a 90% confidence interval for μ1 – μ2. (Use 2 decimal places.)
lower limit      
upper limit      
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