1.

The number of positive integral solutions of x + y + z ≤ 10 is ..................

Answer»

 Let  x + y + z + a = 10 

(where x ≥ 1, y ≥ 1,Z ≥1,a ∈ z&a  ≥ 0 )

Required number = n + r – 1Cr–1

= 7 + 4 - 1C4 - 1  =  10C3

= 10.9.8/1.2.3 = 120



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