If $\alpha =x_1{x}_2{x}_3$ and $\beta =y_1{y}_2{y}_3$ be two three digits numbers, the number of pairs of $\alpha$ and $\beta$ can be formed so that $\alpha$ can be subtracted form $\beta$ without borrowing is

$\alpha =x_1{x}_2{x}_3$ can be subtracted from

$\beta =y_1{y}_2{y}_3$ without borrowing

if $y_3\ge x_3$ and $y_2\ge x_2$ and $y_1\ge x_1$ where $x_1,y_1$ are nonzero digits

No. of pairs $=\left({ }^{10}{C}_1{+}^{10}{C}_2\right)\times \left({ }^{10}{C}_1{+}^{10}{C}_2\right)\times \left({ }^9{C}_1{+}^9{C}_2\right)$

$=\left({55}^2\times 45\right)=3^2\times 5^3\times {11}^2=136125$