9.61 Bass Fishing The pH factor is a measure of the acidity or alkalinity of water. A reading of 7.0 is neutral; values in excess of 7.0 indicate alkalinity; those below 7.0 imply acidity. Loren Hill states that the best chance of catching bass occurs when the pH of the water is in the range 7.5 to 7.9.21 Suppose you suspect that acid rain is lowering the pH of your favourite fishing spot and you wish to determine whether the pH is less than 7.5.

a. State the alternative and null hypotheses that you would choose for a statistical test.

b. Does the alternative hypothesis in part a imply a one- or a two-tailed test? Explain.

c. Suppose that a random sample of 30 water speci- mens gave pH readings with 7.3 and s = 0.2. Just glancing at the data, do you think that the dif- ference x-7.5= -0.2 is large enough to indicate that the mean pH of the water samples is less than 7.5? (Do not conduct the test.)

d. Now conduct a statistical test of the hypotheses in part a and state your conclusions. Test using a = 0.05. Compare your statistically based decision with your intuitive decision in part c.