Most water treatment facilities monitor the quality of their drinking water on hourly basis. One variable monitored it is pH, which measures the degree of alkalinity or acidity in the water. A pH below 7.0 is acidic, one above 7.0 is alkaline, and a pH of 7.0 is neutral.
One water treatment plant has a target pH of 8.5 (most try to maintain a slightly alkaline level).
The mean and standard deviation of 1 hour’s test results, based on 12 water samples at this plant are:

Mean =8.24 S=.16

Does this sample provide sufficient evidence that the mean pH level in the water differs from 8.5?