(a) The mean lifetime of 200 mobile phones in a sample is 1,000 hours and their standard deviation is 130 hours. u is the mean lifetime of all the mobile phones produced. Test the hypothesis that the sample comes from a population whose mean is 1,200 hours at 1% significance level? (b) Consider a random sample of 20 observations. The sample variance is 30.5. Construct a 95% confidence interval for