statistics
posted by heather .
A test of writing ability is given to a random sample of students before and after they completed a formal writing course. The results are given below. Construct a 99% confidence interval for the mean difference between the before and after scores. You may assume the populations are normally distributed.
Before 70 80 92 99 93 97 76 63 68 71 74
After 69 79 90 96 91 95 75 64 62 64 76

For a 99% confidence interval, you can use + or  2.58 from a ztable. You will need to find the correct formula to use for the mean difference.