Question: Twenty students randomly assigned to an experimental group receive an instructional program; 30 in a control group do not. After 6 months, both groups are tested on their knowledge. The experimental group has a mean of 38 on the test ( with an estimated population standard deviation of 3); the control group has a mean of 35 ( with an estimated population standard deviation of 5). Using the .05 level, what should the experimenter the t test for a single sample, but not with the t test for a single sample, but not with the t test for independent means.