A study was designed to investigate the effects of two variables - (1) a student's level of mathematical anxiety and (2) teaching method - on a student's achievement in a mathematics course. Students who had a low level of mathematical anxiety were taught using the traditional expository method. These students obtained a mean score of 470 with a standard deviation of 40 on a standardized test. Assuming a mound-shaped and symmetric distribution, what percentage of scores exceeded 390?
A. approximately 84%
B. approximately 97.5%
C. approximately 100%
D. approximately 95%