> 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