A teacher wants to see if a new unit on taking square roots is helping students learn. She has five randomly selected students take a pre-test and a post test on the material. The scores are out of 20. Has there been improvement? (pre-post) Student 2 3 4 5 Pre-test 11 9 10 14 10 Post- Test 18 17 19 20 18 What is the point estimate of the population mean difference between the pre and post test? Oo O 1.96 Unknown O -7.6