Data Sufficiency

I have a general question with regards to the usage of "or" and "and" in a set theory question. Eg;

A class consists of math or science students. If the total number of the students is 200, how many are science students?

--in trying to find the unknown variables before we determine the sufficiency, do we need to consider the "intersection" of Math and science students for this question? Or, can we consider the intersection to NULL since we say "Math OR science " adn just have the below eq,

Total = Math + Science(basically not considering "Intersection" and"neither"). Appreciate anyones responce.

id suggest that for questions like these you create a 2 column x 2 row matrix like so:

Science Not Science
Math

Not Math
-------------------------------------------------------------
Total Number

Then you can add the given details in the appropriate boxes and find what is needed that way.

Hope this helped.