9.3

5.

(10.117, 30.144)

7.

(9.542, 40.289)

9.

  1. (7.942, 23.66)

  2. (8.59, 20.63). Increasing the sample size decreases the interval width.

  3. (6.61, 31.36). Increasing the confidence level increases the interval width.

11.

(.226, .542) We can say with a 95% level of confidence that the population standard deviation is between .226 and .542

13.

(734.78, 1657.49) We can say with a 90% level of confidence that the population standard deviation is between 734.78 and 1657.49