Quantitative aptitude

Consider the sum modulo 9 ("casting out nines") so that a number becomes equal to the sum of its digits.

Then $A+B+C+D+E+F+G+H+I+J = J+J+J+J$ with the first sum being (0+1+2+3+4+5+6+7+8+9)=45=0 modulo 9. This forces $4J$ and thus $J$ to be divisible by 9.