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The $4$-digit number $32B9$ is divisble by $3$. If $B$ is even, find the digit $B$. 
Overseas Competition->Knowledge Point->Number Theory Modules->Division without Remainders->Divisibility Rules
$$3+2+B+9$$  = 14+B is divisble by 3.  Max single digit possible is 9. Then 14+9 = 23. Range is between 15 to 23.  Multiple of 3 - 3 x 7=21, 3 x 6 =18, 3 x 5 = 15.  Since, it should be even number, 18-14=4. 