You collect data on two independent simple random samples from approximately normal populations. the summary statistics are: n1 = 7, = 7, s1 = 2, n2 = 9, = 4, and s = 1.9. you think the population standard deviations are equal, so you decide to pool the estimates of the population standard deviation of the difference between the means. which of the following gives the correct t statistic for a pooled test of the hypothesis h0 : µ1 − µ2 = 0, and the number of degrees of freedom upon which this is based?