There Are Three Papers Of 100 marks Each In An Examination. Then The No. Of Ways Can A Student Get 150 marks Such That He Gets atleast 60% in Two Papers

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Question

There are three papers of 100 marks each in an examination. Then the no. of ways can a student get 150 marks such that he gets atleast 60% in two papers

Solution

Correct option is

3C2 × 32C2

Therefore,

         Sum of marks obtained = 150

         

The required number of ways

        = No, of integral solutions of (i)

        = Coefficient of x150 in {x60 x61 + …+x100)2 (1+ x + x2+  …+ x30)}         

        = Coefficient of x30 in {(1 + x + … + x40)(1 + x + … + x30)}

        

        = Coefficient of x30 in (1 – x)-3

        = 30 + 3 – C3 – 1 32C2.

Thus, the student gets atleast 60% marks in first two papers to get 150 marks as total in 32C2 ways. But the two papers, of atleast

60% marks, can be chosen out of three papers in 3C2 ways.

Hence the required number of ways = 3C2 × 32C2.

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