Question

11+22+33+....+99=



VA ROG SA MA AJUTATI

Answer 1

11(1+2+3+4+5+6+7+8+9)=11*45=495

Answer 2

$\rm S=11+22+33+...+99\\\\S=11\cdot(1+2+3+...+9)\\\\S=11\cdot(9\cdot10\div2)\\\\S=11\cdot9\cdot5\\\\S=\boxed{495}$