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Title 8.7 Independent random sampling from two normally distributed populations gives the following results: nx = 81; X = 140; s2 X = 25 ny = 100; y = 120; s2 y = 14 Find a 95% confidence interval estimate of the differ- ence between the means of the two populations. 8.8 Assuming equal population variances, determine the number of degrees of freedom for each of the following: a. nx = 16 s2 X = 30 ny = 9 s2 y = 36 b. nx = 12 s2 X = 30 ny = 14 s2 y = 36 C. nx = 20 s2 X = 16 ny = 8 s2 y = 25