Find the number of triples of positive integers satisfying .
Notation : denotes the binomial coefficient , .
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Here we can see that we have x + y + z = 1 0 2 for all + v e integral solutions. We know that if we need to do partitions for n distinct things into 3 divisions and they are non negetive integers then think about lets say there are 1 0 2 balls and we have to divide in 3 divisions . then we need 2 sticks for this division but they can be placed any where so between two sticks we may also get 0 balls. So we see for 1 0 2 balls is we place \(2 ) sticks of partitions then 1 0 3 C 2 are ways to arrange them will be our answer similarly for n balls and r partions our formulae will be n + r − 1 C r − 1 , But ( x , y , z ) is + v e integral then x > 0 , y > 0 and z > 0 or x > = 1 and y > = 1 and z > = 1 or now x − 1 = x ′ , y − 1 = y ′ and z − 1 = z ′ . Hence Now putting x ′ + y ′ + z ′ = 9 9 . From the previous formulae x ′ , y ′ and z ′ are brought for non negetive. Hence our number of triplets ( x , y , z ) for only +ve integers will be 9 9 + 3 − 1 + C 3 − 1 = 1 0 1 C 2 .