Q1) Suppose you require building confidence interval for population mean within some given situation.  Naturally, you should find out whether you must use either t-distribution or z-distribution or possibly even neither based upon information known/gathered in the situation.  Therefore, based upon given information for each situation below, find out which (t-, z- or neither) distribution is suitable  Then if you can utilize either a t- or z- distribution, provide associated critical value (critical t- or z- score) from that distribution to reach given confidence level.

a) 95% confidence n=52 sigma unknown population data believed to be normally distributed.

b) 90% confidence n=7 sigma unknown population data believed to be very skewed.

c) 95% confidence n=85 sigma unknown population data believed to be skewed right.

d) 99% confidence n=15 sigma unknown population data believed to be normally distributed.