A professor is interested in comparing the average amount spent on textbooks for freshmen and sophomores. A random sample of 8 freshmen yielded a sample mean amount of $1013 and a sample standard deviation of $75. A random sample of 8 sophomores yielded a sample mean amount of $1234 and a sample standard deviation of $340. Construct a 99% confidence interval for the difference between the mean amount spent on textbooks by freshmen and the mean amount spent by sophomores (ie. do freshmen minus sophomores). Since the sample standard deviations are wildly different, use a method which does not assume the populations have the same variance.

What is the appropriate degrees of freedom in this case? Give your answer to four decimal places.

What is the lower confidence limit on the interval? Give your answer to two decimal places.

What is the upper confidence limit on the interval? Give your answer to two decimal places.

Using this interval, is it reasonable to conclude that the average sophomore spends more than the average freshman?

Yes because the upper endpoint on the interval is below 0.
Yes because the upper endpoint on the interval is above 0.
No because the interval contains 0.
Yes because the interval contains 0.