A Tutor Promises to Improve GMAT Scores of Students by More

Multiple Choice

A tutor promises to improve GMAT scores of students by more than 50 points after three lessons.To see if this is true,the tutor takes a sample of 49 students' test scores after and before they received tutoring.The mean difference was 53 points better after tutoring,with a standard deviation of the difference equal to 12 points.Let µ_D denote the mean of the difference: score after tutoring minus score before tutoring.Which of the following hypotheses will determine if the students improved their test scores by more than 50 points after being tutored?

A) H₀: µ_D ≤ 0,H_A: µ_D > 0
B) H₀: µ_D ≥ 0,H_A: µ_D <0
C) H₀: µ_D ≤ 50,H_A: µ_D >50
D) H₀: µ_D ≥ 50,H_A: µ_D <50