The amount of PCBs was measured in 40 samples of soil that were treated with contaminated sludge. The following summary statistics were obtained.
 = 3.56 s = .5 ppm
(a) Perform a test of hypotheses with the intent of establishing that the mean PCB contamination is less than 3.7 p.p.m. Take α = .05.
(b) What error could you have possibly made in part(a)?