Twelve teachers attended a seminar on mathematical problem solving. Their attitudes were measured before and after the seminar. A positive number change attitude indicates that a teacher's attitude toward math became more positive. The twelve change scores are as follows: 3; 8; -1; 2; 0; 5; -3; 1; -1; 6; 5; -2

a. What is the average change score?

b. What is the standard deviation for this population?

c. What is the median change score?

d. Find the change score that is 2.2 standard deviations below the mean.