From two normal populations assumed to have the same variance, independent ran-dom samples of sizes 15 and 19 were drawn. The first sample (with n1 5 15) yielded mean and standard deviation 111.6 and 9.5, respectively, while the second sample (n2 5 19) gave mean and standard deviation 100.9 and 11.5, respectively. The esti-mated standard error of the difference in sample means is .