Problems from Phantom sums

Development:

First of all we write the sum as a table:

$7$	$A$	$4$
$1$	$2$	$C$
$B$	$6$	$1$

In the last column, we have the sum $$4+C=11$$

as $C$ is said to be positive, the result is $11$, and $C$ should be $7$ so that the result is $11$.

We kept a $1$ so the second column becomes: $$A+2+1=6\to A+3=6$$

then $A$ should be $3$ so that the result is $6$.

Finally, given that now we didn’t need any extra one: $$7+1=B$$

Therefore, $B$ should be $8$.

Solution:

$A=3,B=8C=7$

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