Tìm x,y ∈ Z $\frac{1}{18}$ < $\frac{8}{12}$ <$\frac{9}{9}$ <$\frac{1}{4}$

Đáp án:

$\frac{9}{36}$ < $\frac{3x}{36}$ <$\frac{4y}{36}$ <$\frac{9}{36}$

=> 2 <3x<4y<9

=> (x,y)∈ { (1;1);(1,2);(2,3)}