3. A phone industry manager thinks that customer monthly cell phone bill have increased, and now average over SR 80 per month. (Given s-9). The company wishes to test this claim and sample results are...

Extracted text: 3. A phone industry manager thinks that customer monthly cell phone bill have increased, and now average over SR 80 per month. (Given s-9). The company wishes to test this claim and sample results are given below: n = 81, = 81.2 . Test the hypotheses at significance level a = 0.05.