Two confidence intervals. The data used for Exercise 10.47 include 195 men 30 years old. The mean income of these men is y 5 $49,880 and the standard deviation of these 195 incomes is sy 5 $38,250.

(a) Use the one-sample t procedure to give a 95%

confidence interval for the mean income y of 30-year-old men.

(b) Why is this interval different from the 95%

confidence interval for y in the regression output?

(Hint: What data are used by each method?)