An evaluator is assessing the benefits gained from two different methods of teaching technical mathematics to employees. Group 1 receives training in a standard lecture format, while group 2 receives instruction from an interactive computer program. The average score for the first group is 90, with a standard deviation of 6.4, and for the second group the average score is 72 with a standard deviation of 3.6. The first group has 52 members and the second group 38 members. The null hypothesis is that the population means are equal, and the population variances are assumed to be equal. What is the pooled sample standard deviation? O 5.40 O 9.12 O 22.48 O 7.36