Question

cat face 2+4+6+...+240?

Answer 1

$\displaystyle 2+4+6+...+240=2(1+2+3+...+120)=2 \times \frac{120(120+1)}{2} = \\ \\ =2\times \frac{120 \times 121}{2} =\not2 \times \frac{14520}{\not2} =14520$