Section 9.3

#13. Given info: n_{1} = 64, Xbar_{1} = 53.3, s_{1} = 3.6, n_{2} = 65, Xbar_{2} = 51.3, s_{2} = 4.5 .

We are to test if light users (group 1) have a higher mean than heavy users (group 2), so H_{1} has to be µ_{1}-µ_{2} > 0, so that means H_{0} must be µ_{1}-µ_{2} = 0.

#14. This uses the same info as on #13, but it is a confidence interval problem. Look in your book for the confidence interval formula for the difference of two means.