30-35 You measure the lifetime of a random sample of 64 tires of a certain brand. The sample mean is 40 months. Suppose that the lifetimes for tires of this brand follow a normal distribution, with...

Extracted text: 30-35 You measure the lifetime of a random sample of 64 tires of a certain brand. The sample mean is 40 months. Suppose that the lifetimes for tires of this brand follow a normal distribution, with unknown mean u and standard deviation of 5 months. 35. A 98% confidence interval for u is a. 49.80 to 50.20. b. 38.55 to 41.45. c. 48.64 to 51.36. d. 40.2 to 59.8.