I think it is $ \frac {102.101}{ 2} $. Notice if you get o in physics then you will have only one way to get 200 marks in the three subjects.if you get 1 in physics then you will have 2 ways and for 2 you will have 3 ways and it will go on for o to 100 ..It forms a series that
$ 1+2+3+.............+101$ and the sum of the series is $ \frac {102.101}{2} $...