Divisible by 9

The four digit numeral 3AA1 is divisible by 9.What digit does A represent?

MetroEye: If a number is divisible by 9, the sum of digits should also be divisible by 9

=> 3+A+A+1=4+2A should be divisible by 9
If 4+2A=9, then A=2.5 which is not integer.
If 4+2A=18, then A=7 which is an integer.

So A represents digit 7.