# problem-8.28

problem-8.28 The assumptions are such that the t-statistic can be used to compute the small p-value. We assume that the population variances are equal.

    > xbar1 =79; xbar2 = 110
    > n1 = n2 = 250
    > s1 = 25; s2 = 20
    > sp = sqrt(( (n1-1)*s1^2 + (n2-1)*s2^2 )/(n1+n2-2))
    > SE = sp * sqrt(1/n1 + 1/n2)
    > T = (xbar1 - xbar2)/SE
    > 2 * pt(T, df = n1+n2-2)       # T is negative, two sided
    [1] 1.224e-43