Mr B is a teacher at a high school, who is occasionally late for this classes.
Mr B teaches two subjects, Chemistry and Physics. It is known that he's late 10% of the time for Chemistry and 15% of the time for Physics. Rumors from student said that Mr B was late again.. What is the probability this is rumor came from a Chemistry student. Assuming that 75% are doing Chemistry and 25% are doing Physics. (Note: no students take both subjects)