If we say [tex]13 ?349[/tex] is divisible by [tex]3[/tex].
It means that the sum of the digits of [tex]13 ?349[/tex] is divisible by [tex]3[/tex].
To check this,
[tex]1 + 3 + ? + 3 + 4 + 9[/tex]
[tex]20 + ?[/tex]
We know that [tex]20[/tex] is not divisible by [tex]3[/tex] and hence the digit cannot be [tex]0[/tex].
Now the digits that are possible in this situation are [tex]1,4[/tex] and [tex]7[/tex].
