Do the data in Exercise 9.22 substantiate the conjecture that the true standard deviation of the acidity measurements is larger than 0.4? Test at a = .05.

Data from in Exercise 9.22

Measurements of the acidity (pH) of rain samples were recorded at 13 sites in an industrial region.

Determine a 95% confidence interval for the mean acidity of rain in that region.

3.5 5.1 5.0 3.6 4.3 4.2 4.5 4.8 4.9 4.7 3.6 4.8 4.7