Which of the following is a true statement? The population standard deviation is always known. It is appropriate to use normal distribution to compute the confidence interval for population mean. The population standard deviation is usually not known. It is appropriate to use t distribution to compute the confidence interval for population mean. Question 3 1 pts A sample of 123 people aged 18-22 reported the number of hours they spent on the internet in an average week. The sample mean was 7.28 hours, with a sample standard deviation of 3.65 hours. Assume this is a simple random sample from the population. Use the technology covered in the videos to construct a 95% confidence interval for u, the population mean number of hours per week spent on the internet in that age group. Which distribution was used in this problem? Enter Z for normal distribution or T for t-distribution. What is the margin of error you found? What is the standard error you found? What is the lower bound of the confidence interval? What is the upper bound of the confidence interval? Question 4 1 pts Scientists want to estimate the mean weight of mice after they have been fed a special diet. A sample of 72 mice have been weighed, and the standard deviation was s = 2.18 grams. Estimate the number of mice that must be weighed for a 94% confidence interval to have a margin of error of 0.4 grams