Let and be positive integers satisying the equation above, then find the number of ordered triplets .
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x + y + 3 z = 2 7 x + y = 2 7 − 3 z
Since x , y and z are positive integers, the only permissible values of z = { 1 , 2 , 3 , ⋯ , 8 }
When z = 1 , x + y = 2 4 and the number of ordered pairs ( x , y ) satisfying this equation = 2 4 − 1 C 2 − 1 = 2 3 C 1 .
When z = 2 , x + y = 2 1 and the number of ordered pairs ( x , y ) satisfying this equation = 2 1 − 1 C 2 − 1 = 2 0 C 1 .
When z = 3 , x + y = 1 8 and the number of ordered pairs ( x , y ) satisfying this equation = 1 8 − 1 C 2 − 1 = 1 7 C 1 . ⋮
When z = 8 , x + y = 3 and the number of ordered pairs ( x , y ) satisfying this equation = 3 − 1 C 2 − 1 = 2 C 1 .
So, the total number of waying of finding the ordered triplets ( x , y , z ) = 2 3 C 1 + 2 0 C 1 + 1 7 C 1 + ⋯ + 2 C 1 = 2 3 + 2 0 + 1 7 + ⋯ + 2 = 1 0 0