12. Dissolved O2 Content Water samples were taken at four different locations in a river to determine whether the quantity of dissolved oxygen, a measure of water pollution, varied from one location to another. Locations 1 and 2 were selected above an industrial plant, one near the shore and the other in midstream; location 3 was adjacent to the industrial water discharge for the plant; and location 4 was slightly downriver in midstream. Five water specimens were randomly selected at each location, but one specimen, corresponding to location 4, was lost in the laboratory. The data and a MS Excel analysis of variance computer printout are provided here (the greater the pollution, the lower the dissolved oxygen readings).

a. Do the data provide sufficient evidence to indicate a difference in the mean dissolved oxygen contents for the four locations?

b. Compare the mean dissolved oxygen content in midstream above the plant with the mean content adjacent to the plant (location 2 versus location 3). Use a 95% confidence interval.

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Location Mean Dissolved Oxygen Content 1 5.9 6.1 6.3 6.1 6.0 2 6.3 6.6 6.4 6.4 6.5 3 4.8 4.3 5.0 4.7 5.1 4 6.0 6.2 6.1 5.8