Mary has taken 7 quizzes in her social studies course. she received the following grades on the quizzes: 94, 74, 78, 90, 85, 82, 78 which statement about mary's grades is true? a. the mean and median are equal. b. the mean and mode are equal. c. the median is 82 and the mode is 78. d. the mean is 83 and the median is 90.