A test of water safety is to be performed. An ecologist plans to sample drinking water in several locations in a residential area and measure the concentration of certain dangerous chemicals. Drinking water is considered safe when the concentration of those chemicals is below 100 units per liter. (a) What null and alternative hypotheses should the ecologist use to address the problem? (b) A random sample of 30 water sources in this area produced a mean concentration of 110 units/l with standard deviation 20 units/l. Perform the appropriate test of the hypotheses you formulated in question (a) and find out whether the water is safe to drink.