1. The manufacturer of batteries used in small electric appliances wants to esti- mate the average life of a battery. A random sample of 12 batteries yields x = 34.2 hours and s = 5.9 hours. Give a 95% con?dence interval for the average life of a battery.

2. A tire manufacturer wants to estimate the average number of miles that may be driven on a tire of a certain type before the tire wears out. A random sample of 32 tires is chosen; the tires are driven on until they wear out, and the number of miles driven on each tire is recorded. The data, in thousands of miles, are as follows:

32, 33, 28, 37, 29, 30, 25, 27, 39, 40, 26, 26, 27, 30, 25, 30, 31, 29, 24, 36, 25, 37, 37, 20,  22,

35, 23, 28, 30, 36, 40,  41

Give a 99% con?dence interval for the average number of miles that may be driven on a tire of this kind.