8a, 8b, 9, 10, 11a, b, c, d

8. In a simple random sample of 100 electronic components produced by a certain method, the mean lifetime was 125 hours. Assume that component lifetimes are normally distributed with population standard deviation of 20 hours. a) Construct a 98% confidence interval for the mean battery life. b) Find the sample size needed so that a 99% confidence interval will have a margin of error of 3. 9. TRUE or FALSE: The Student's t curve is less spread out than the standard normal curve. 10. TRUE or FALSE: The Student's t distribution should not be used to find a confidence interval for the population mean if outliers are present in a small sample. 11. Find the critical value needed to construct a confidence interval of the given level with the given sample size. a) Level 90%, sample size 6 b) Level 98%, sample size 12 c) Level 95%, sample size 32 d) Level 99%, sample size 10