Question

11x+18y = 120.tìm số nguyên dương x,y

Answer 1

Ta có: 11x+18y=11(x+y)+9y=120

Do 120 chia 11 dư 10, 11(x+y)\(⋮\)11 => 7y chia 11 dư 10, 9y<120

=> 7y\(\in\){7;14;21;28;35;42;49;56;63;70;77;84;91;98;105;112}

Do 98 chia 11 dư 10 => 7y=98 => y=14

=> 11(x+y)=22 => x+14 = 2 (vô lý)

Do 21 chia 11 dư 10 => 7y=21 => y=3

=> 11(x+y)= 99 => x+3=9 => x=6

Vậy x=6, y=3