with complete solution typewritten much better 12-15

13. The study referenced in Problem 1 talked to teens in smaller focus Groups, but also interviewed additional teens over the phone. When the study was complete, 588 teens had answered the question about their Facebook friends with 500 teens saying that they have more than 500 friends. Find a 90% confidence interval for the true proportion of teens that would report having more than 500 Facebook friends based on this larger sample. Compare the results to those in Problem 1. 14. A process has been developed that can transform ordinary iron into a kind of super iron called metallic glass. Metallic glass is three to four times stronger than the toughest steel alloys. To estimate the mean temperature at which a particular type of metallic glass becomes brittle, 20 pieces of this material were randomly sampled from a recent production run. Each piece was subjected to higher and higher temperatures until it became brittle. The temperature at which brittleness first appeared was recorded for each piece in the sample. The following results were obtained: x_ = 500 F, s = 15 F. Calculate the length of the 95% condence interval for the mean temperature at which a particular type of metallic glass becomes brittle. 15. A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what sample size should be taken so that, at 95% condence, the margin of error will be 2 months or less. 12. Malayan Colleges of Mindanao recently conducted a study analyzing the privacy management habits of teen internet users. In a group of 50 teens, 41 reported having more than 500 friends on Facebook. Find a 90% confidence interval for the true proportion of teens who would report having more than 500 Facebook friends