For Exercises 49–56, do the following:

  1. State the hypotheses.
  2. Find and the critical region.
  3. Find . Also, draw a standard normal curve showing , the critical region, and .
  4. State the conclusion and the interpretation.

Question 9.90

55. Americans' Height. A random sample of 400 American adults yields a mean height of 176 centimeters. Assume . Conduct a hypothesis test to investigate whether the population mean height of American adults has changed from 175 centimeters, using level of significance .

9.2.55

(a) (b) . Reject if or if . (c) .

image

(d) Since is , the conclusion is reject . There is evidence at the 0.10 level of significance that the population mean height of Americans has changed from 175 centimeters.