For Exercises 14 and 15, perform the following steps:

  1. State the hypotheses and the rejection rule for the -value method.
  2. Calculate .
  3. Find the -value. Draw the standard normal curve, with and the -value indicated on it.
  4. State the conclusion and the interpretation.

Question 9.400

15. We want to test, at level of significance , whether the population mean is less than −10. A random sample of size 25 is taken from a normal population. The sample mean is −12. Assume .

9.99.15

(a) . Reject if the . (b) −5 (c)

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(d) Since the , reject . There is evidence that the population mean is less than −10.