Statistics Help!?

Question

In healthy adults the average pH of spinal fluid is 7.39
From a sample of unhealthy 44 patients with the mean spinal fluid was 7.26 with a standard deviation of 0.17. Can we conclude, at the 0.5 level of significance, that the pH of unhealthy patients is different from the pH for healthy patients? Explain.

Answer 1

Z = (7.26-7.39)/0.17 = -13/17

If 0.5 level of significance critical value = 0.6745
13/17 = 0.764

So at 0.5 level of significance you can conclude the pH of unhealthy patients is different. (since the 0.764 > 0.6745 critical value. The sign does not matter since it is a 2- tailed test)