In the Department of Mathematical and Computational Science, 83% of lecture halls have chalkboards, and the other 17% have dry-erase boards. Of the classes taught in rooms with chalkboards, 75% are mathematics courses, 15% are computer science courses, and 10% are statistics courses. Of the classes taught in rooms with dry-erase boards, 65% are computer science courses, 8% are mathematics courses, and 27% are statistics courses. What percentage of courses at the college are mathematics or statistics? Identify the probability law/s used if any.