Answer :

We know that if , then one of the following conditions need to be satisfied:


i. p = q


ii. n = p + q


Let us use condition (i),


3r = r + 3


2r = 3





We know that for a combination nCr,r≥0 and r should be an integer, which is not satisfies here,


So, the condition (ii) must be satisfied,


15 = 3r + r + 3


4r = 12



r = 4.


The value of r is 4.


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