# Do you know subtraction??

Discrete Mathematics Level pending

Let $$n_1= x_1x_2x_3\quad and \quad n_2= y_1y_2y_3$$ be two 3-digit numbers.How many pairs of $$n_1$$ and $$n_2$$ can be formed so that $$n_1$$ can be subtracted from $$n_2$$ without borrowing?

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