4.22. Suppose we wish to test the hypotheses Ho: =15 H: #15 where we know that o = 9.0. If the true mean is really 20, what sample size must be used to ensure that the probability of type II error is no greater than 0.10? Assume that = 0.05. (Use the OC curve chart in Figure 4.7 below) 1.0 0.8 0.6 0.4- 0.2 100 3 4 5 FIGURE 4.7 Operating-characteristic curves for the two-sided normal test with = 0.05. (Reproduced with permission from C. L. Ferris, F. E. Grubbs, and C. L. Weaver, "Operating Characteristic Curves for the Common Statistical Tests of Significance," Annals of Mathematical Statistics, June 1946.)