Use the data on education from Chapter 6, Exercise 5.

a. Construct the 95% confidence interval for the mean number of years of education for lower-class and middle-class respondents.
b. Construct the 99% confidence interval for the mean number of years of education for lower-class and middle-class respondents.
c. As our confidence in the result increases, how does the size of the confidence interval change? Explain why this is so.

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Lower class Working class Middle class Upper class Mean 11.61 12.80 14.45 15.45 Standard Deviationn 2.67 2.85 3.08 2.98 123 626 38