7.09 Consider iid random variables X1, ..., Xn of mothers' ages in years arising from a population with mean / and variance o?. Corresponding to 7.5. EXERCISES 163 Xi, is the age Yi in years of the mother's eldest child. The ages of eldest children who have mothers that are still alive arise from a distribution with mean /2 and variance o?. There is interest in testing Ho : #1 - #2 = 20 versus H1 : M1 - /2 > 20. Approximately how large should n be such that the power of the test is 0.90 when /1 - /2 = 25 years? You will need to make an assumption concerning variances; try to make it realistic