9. There is a certain industrial setting in which many years of data indicated that the average a worker made 22.5 assembly errors daily (with a standard deviation of 9.2). An engineering psychologist noted several design modifications that she believed would decrease errors while maintaining high production levels. A sample of 50 workers was trained to use the modied system, and on the designated test day these workers averaged 19.2 assembly errors. Did the modified system decrease errors? [25 total points] a. Describe the statistical test to be done. [2 points] b. State the null and alternative hypotheses. [2 points] c. What is the critical value of the test statistic? What is the decision rule for rejecting the null hypothesis? Draw the picture of the rejection region. [2 points] CV: Reject H0 if z