Here consider the equation as : y+z=20-2x Here x can be 1,2,......9 let xbe a parameter that is r. Number of positive solutions are =20-2r Therefore required number=Summatin from r=1to r=9;20-2r =20*9-2*(9*10/2)=90. Answer is 90. Don't forget to rate my answer.............
Moderation Team
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