# Probability: 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.

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Standard Error of Difference in Sample Means and Confidence Intervals are investigated.

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