Hi can you help me with these questions a b c and d)registered for either maths class or chemistry class but not both.Thanks

Q2. In a group of 80 students, 50 of them registered for Mathematics class, 15 of them registered for Chemistry class and 5 of them registered for both classes. A student is selected at random from the group. Find the probability that the student (a) registered for Mathematics class or Chemistry class, (2 marks) ( b ) registered for Chemistry class if he registered for Mathematics class, (2 marks) (c ) does not register for Mathematics class, given that he registered for Chemistry class,