A company that dumps its industrial waste into a river has to meet certain restrictions. One particular constraint involves the minimum amount of dissolved oxygen that is needed to support aquatic life. A random sample of 10 specimens taken from a given location gives the following results of dissolved oxygen (in parts per million, ppm):

(a) Find a two-sided 95% confidence interval for the mean dissolved oxygen, and interpret it.
(b) What assumptions do you need to make to answer part (a)?
(c) Suppose that the environmental standards stipulate a minimum of 9.5 ppm of average dissolved oxygen. Is the company violating the standard? Test at a level of significance a of 0.05.

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9.0 8.6 9.2 8.4 8.1 9.5 9.3 8.5 9.0 9.4