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One hundred teachers attended a seminar on mathematical problem solving. The attitudes of representative sample of 12 of the teachers were measured before and after the seminar. A positive number for change in attitude indicates that a teacher’s attitude toward math became more positive. The twelve change scores are as follows.

4; 8; ?1; 2; 0; 5; ?3; 1; ?1; 6; 5; ?2

• Part (a)
• What is the mean change score? (Round your answer to two decimal places.)

• Part (b)
• What is the standard deviation for this sample? (Round your answer to two decimal places.)
• 3.54