10.33 Soil pH is an important variable in the design of structures that will contact the soil. The pH at a potential construction site was said to average 6.5. Nine test samples of soil from the site gave readings of 7.3, 6.5, 6.4, 6.1, 6.0, 6.5, 6.2, 5.8, 6.7 Do these readings cast doubt upon the claimed average? (Test at the 5% significance level.)

What assumptions are necessary for this test to be valid?