A random sample of four students who took the sat test twice had the following math scores: Student 1: 450, 440; student 2: 520,600; student 3: 720,720; and student 4: 600,630 Assume that the change in math say score (second score-first score) for the population of all students taking the test twice is normally distributed with mean. Find the sample estimate for the mean of this population (the change in math SAT score)