Hi PiyaNca,

To start, you would likely receive more of a response if you posted your question in the appropriate sub-forum. For example, the Problem Solving Forum can be found here:

https://www.beatthegmat.com/problem-solving-f6.html

In this question, we're told that to earn a joint degree, a student must take any two maths classes (from 8 classes that are offered) and any two physics classes (from 9 physics classes that are offered). We're asked for the number of different combinations of classes to get a joint degree.

Since we're dealing with COMBINATIONS of classes, the 'order' of the classes does NOT matter. We can use the Combination Formula to answer this question.

N!/K!(N-K)! where N is the total number of classes and K is the number in the sub-group.

For the 8 math classes, there are 8!/2!6! = (8)(7)/(2)(1) = 56/2 = 28 possible groups of 2 classes
For the 9 physics classes, there are 9!/2!7! = (9)(8)/(2)(1) = 72/2 = 36 possible pairs of 2 classes
Thus, the total number of combinations is (28)(36) = 1008

Final Answer: D

GMAT assassins aren't born, they're made,
Rich