54 WORKING WITH SAMPLE DATA Answer H 0 : $27.61 Average sales per customer transaction is less than or equal to $27.61. H 1 : > $27.61 Average sales per customer transaction is greater than $27.61. Because the population value is not known, we use the sam- ple value s to approximate it. So we use the t- distribution, not the z- distribution. Decision Rule: Since this is a one-tailed test, the alpha level of 0.01 is entirely in the upper tail of the rejection region. See Figure 4.1. For = 0.01 with 59 degrees of freedom, we will reject the null hypothesis if the calculated test statistic falls above t = 2.391. Test Statistic: