The shaded region of the first diagram represents the event that the student is taking a course in calculus. That of the second diagram represents the event that the student is not taking a course in calculus. The shaded area of the third diagram represents the event that the student is taking a course in calculus and/or a course in applied mechanics. Finally, that of the fourth diagram represents the event that the student is taking a course in calculus as well as a course in applied mechanics.