Confidence interval for true population means and sample size.
1) A researcher wishes to estimate the proportion of executives who own a car phone. She wants to be 90 percent confident and be accurate within 5 percent of the true proportion. Find the minimum sample size necessary.
2) A survey of 30 adults found that mean age of a person's primary vehicle is 5.6 years. Assume that the standard deviation of the population is 0.8 year, find a 99 percent confidence interval of the population mean age. prepare a sentence that interprets this interval.