Question

Replace A, B by suitable numerals.
$$\begin{gathered} \begin{array}{ccc}& 6& A\\ -& A& B\end{array} \\ \overline{\underline{\begin{array}{ccc}& 3& 7\end{array}}} \end{gathered}$$

Answer 1

First look at the left column, which is:
$6-A=3$

This implies that the maximum value of A can be 3.

$A\le 3$ ... (1)

The next column has the following:
$A-B=7$

To reconcile this with equation (1), borrowing is involved.

We know:
$12-5=7$

∴ $A=2andB=5$