Question: A sample of n = 25 college students was given a problem-solving task at noon on one day. For each student, the difference between the first and second score was recorded. For this sample, the students averaged Md = 4.7 points better on the first test with a variance of s squared = 64 for the difference scores.

a. Do the data indicate a significant change in problem-solving ability? Use a two-tailed test with a = .05.

b. Compute an estimated Cohen’s d to measure the size of the effect.