a) Average total daily sales at a small food store are known to be $451.75. The store manager recently made some changes in displays of goods, order within aisles, and other changes, and she now wants to know whether average sales volume has increased. A random sample of 14 days shows Xbar = $502.95 and s = $64.00. You can assume normality. Using alpha = 4%, is the sampling result significant? Explain.

(b) A simple random sample of 350 households from a large community was selected to estimate the mean residential electricity usage per household during January of last year. Another simple random sample of 420 households was selected, independently of the first, to estimate mean residential electricity usage during January of this year. The sample results (expressed in kilowatt hours) were:

Last Year Sample size 350 Sample mean 1272 kwh Sample sd 259 kwh

This Year Sample size 420 Sample mean 1335 kwh sample sd 265 kwh

You feel that the mean usage of electricity has increased for January of this year compared to January of last year. Carry out the appropriate hypothesis test at 5%.