The breaking strength of a fiber is required to be at least 150 psi. Past experience has indicated that the standard deviation of breaking strength is ???? = 3 psi. A random sample of four specimens is tested, and the results are y1 = 145, y2 =

153, y3 = 150, and y4 = 147.

(a) State the hypotheses that you think should be tested in this experiment.

(b) Test these hypotheses using ???? = 0.05. What are your conclusions?

(c) Find the P-value for the test in part (b).

(d) Construct a 95 percent confidence interval on the mean breaking strength.