A sales manager of a hardware warehouse monitors sales trends in the plumbing section by monitoring the sales recorded invoices at the end of each month. Hadonically, the sales invoice values are normally distributed, and the average sales invoice value has been stable at $120,

Last month, the sales recorded on a random sample of 12 sales invoices yielded an average of $111.81 with a standard deviation of $20.82 Does this evidence support at the 5% level of significance the contention that the average sales invoice value has decreased? Use the following template to the at your concluse

Step 1. Statement of the hypotheses (2 marks)

Step 2. Test statistic and the standardised test statistic (0.5 mark)

Step 3. Level of significance (0.5 mark)

Step 4. Decision rule (2 marks)

Step 5. Computation of the value of the test statistic (2 marks)

Step 6. Conclusion (3 marks)