A sample of twenty newborn elephants had a sample mean of 225 pounds and a sample standard deviation of 15 pounds. However, it is known that the standard deviation for the population (sigma) is...

A sample of twenty newborn elephants had a sample mean of 225 pounds and a sample standard deviation of 15 pounds. However, it is known that the standard deviation for the population (sigma) is actually 18 pounds. Construct a 90% confidence interval for the weight of newborn elephants.

Lower_______pounds

Upper_______pounds

Is it best to use a Z-interval or a T-interval?