A tutor promises to improve GMAT scores of students by more than 60 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 63 points better after tutoring, with a standard deviation of the differences equal to 12 points. Let )/p denote the mean of the difference: score after tutoring minus score before tutoring, Which of the following is the correct value of the test statistic? Multiple Choice O 2 = 1.7143 O 2 = 1. 7500 O t48 - 1. 7143 O +48 = 1.7560