Standard Error of Difference in Sample Means and Confidence Intervals

Aggregate with a low measre of thermal conductivity is desirable for paving. Two types of aggregate are randomly sampled and tested fir thermal conductivity, with 25 observations from X (lower cost type) with mean 0.485 and standard deviation 0.18, and 25 observations from Y (higher cost type) with mean 0.372 and standard deviation 0.16.
(a) Find the standard error of the difference in the sample means bar-X - bar-Y.
Var(bar-X - bar-Y) =
The standard error is...

b) Obtain a 99% CI for the mean difference.

Please see the attached file for the fully formatted problems.

Attached file(s):

Q10.doc  View File