You would like to construct a 90% confidence interval to estimate the population mean score on a nationwide examination in psychology, and for this purpose we choose a random sample of exam scores. The sample we choose has a mean of 486 and a standard deviation of 70. (a) What is the best point estimate, based on the sample, to use for the population mean? (b) For each of the following sampling scenarios, determine which distribution should be used to calculate the critical value for the 90% confidence interval for the population mean. (In the table, Z refers to a standard normal distribution, and t refers to a t distribution.) Could use Sampling scenario Unclear either Z ort The sample has size 13, and it is from a population with a distribution about which we know very little. The sample has size 17, and it is from a normally distributed population with an unknown standard deviation. The sample has size 105, and it is from a non-normally distributed population with a known standard deviation of 75.