Question

If $345A7$ is divisible by $3$, supply the missing digit in place of ${}^{\prime }{A}^{\prime }$

Answer 1

A number is divisible by $3$ when the sum of digits of the number is divisible by $3$.
Now, $3+4+5+A+7=19+A$
we can see that this sum can be $21,24,27$
So, either $A=2,A=5,A=8$