State the degrees of freedom used in this test? Write the formula for the pooled variance and interpret it. What is the formula for the test statistic? Unknown Variances, Assumed Equal tcalc=n1sp2+n2sp2where(x1x2)sp2=n1+n22(n11)s12+(n21)s22 For critical value, use Student's twith d.f. =n1+n22.