Polychlorinated biphenyls (PCB's) are used in the manufacture of electrical transformers and pose a great danger to health when released into the environment. The PCB concentration (in parts per million, ppm) was measured in samples of fish from two rivers:
River A 8.1 7.7 8.3 9.1 7.1 7.8 8.3 6.4 8.1 7.2
River B 6.5 6.3 5.3 4.2 5.6 5.6 5.5 6.0
(a) Test at alpha = .01 if the mean PCB concentration in fish is significantly higher for river A.
(Use Excel to find x, s2 , y, s2 then do the rest by hand)
(b) Estimate the mean difference PCB concentration for the fish in the two rivers using a 99% confidence interval.