1.	Assume you need to build a confidence interval for a population mean within some given situation. Naturally, you must determine whether you should use either the t-distribution or the z-distribution or possibly even neither based upon the information known/collected in the situation. Thus, based upon the information provided for each situation below, determine which (t-, z- or neither) distribution is appropriate. Then if you can use either a t- or z- distribution, give the associated critical value (critical t- or z- score) from that distribution to reach the given confidence level.
a.	98% confidence	n=150	unknown	population data believed to be normally distributed
Appropriate distribution:
Associated critical value:
b.	90% confidence	n=12	unknown	population data believed to be normally distributed
Appropriate distribution:
Associated critical value:
c.	95% confidence	n=18	unknown	population data believed to be skewed left
Appropriate distribution:
Associated critical value:
d.	99% confidence	n=75	known	population data believed to be very skewed
Appropriate distribution:
Associated critical value: