In testing whether the means of two normal populations are equal, summary statistics computed for two independent samples are as follows: Brand X Brand Y n1=20 n2=20 x1 bar 7.30 x2 bar=6.80 s1=1.10 s1=1.15 Assume that the population variances are equal. Then, the standard error of the sampling distribution of the sample mean difference x??1−x??2 is equal to