Enrollment in finite mathematics plus enrollment in calculus is less than 300.
The first step in solving a word problem is identifying the variables. The variables in any algebraic expression is the unknown value, and to solve it we usually assign a letter to represent it (x and y being the most commonly used).
In the question above, we already know that the number of student enrollees is less than 300 and not equal to 300 (might as well be just 20, we do not know) but we do know that it is NOT EQUAL TO 300, but less than.
Also we do not know the number of those enrolled for finite mathematics, so we shall call that f. Those that enrolled for calculus we shall call c. Since both categories are less than 300, the two variables f and c can now be written as an inequality which reads,
f plus c is less than 300
That is;
f + c ⊂ 300