In a class of 450 students, 300 are taking a mathematics course and 260 are taking a science course. If 140 of these students are taking both courses, how many students are not taking either of these courses?
(1) 30 (3) 110
(2) 40 (4) 140
I know there is a formula or equation for "EITHER" questions such as this one.
What is a good formula or equation to use to find the answer?