Solution to Exercise 7.37 (a).

  The CI (Confidence Interval) is

$$\bar{x} \, \pm \, t_{\alpha/2, n-1} * s/\sqrt{n} \; = \; 0.9255 \, \pm \, 2.093 * .0181 .$$

See the solution of the previous problem 2 for a brief discussion of the left hand side. Note that Minitab gives us the ``standard error'' of the mean

$$s/\sqrt{n} \; = \; .0809/\sqrt{20} \; = \; 0.01808979 \; = \; .0181 ,$$

so we don't even have to do that one. Plugging and chugging, the final answer is

$$0.9255 \pm .0378833 \; = \; (0.05467,0.13043) .$$

WHOOPS - arithmetic error there. The final result should read (0.88762,0.96338), or (0.888,0.963).

3/31/2001