Question

Industrial wastes and sewage dumped into our rivers and streams absorb oxygen and thereby reduce the amount of dissolved oxygen available for fish and other forms of aquatic life. One state agency requires a minimum of 5 parts per million (ppm) of dissolved oxygen in order for the oxygen content to be sufficient to support aquatic life. A pollution control inspector suspected that a river community was releasing amounts of semitreated sewage into a river. To check his theory, he drew five randomly selected specimens of river water at a location above the town, and another five below. The dissolved oxygen readings (in parts per million) are as follows.

Above Town	4.7	5.2	5.0	4.8	5.2
Below Town	4.9	4.6	4.8	4.8	5.0

(a) Do the data provide sufficient evidence to indicate that the mean oxygen content below the town is less than the mean oxygen content above? Test using α = 0.05. (Use μ₁ for the population mean for the above town location and μ₂ for the population mean for the below town location.)

State the test statistic. (Round your answer to three decimal places.)
t =  
State the rejection region. (If the test is one-tailed, enter NONE for the unused region. Round your answers to three decimal places.)

t >  

t <
State the conclusion.

(b) Suppose you prefer estimation as a method of inference. Estimate the difference in the mean dissolved oxygen contents (in ppm) for locations above and below the town. Use a 95% confidence interval. (Use μ₁ − μ₂. Round your answers to three decimal places.)
ppm to  ppm

Answer 1