Question

Efectuati 2+4+6+....+50

Answer 1

$\displaystyle 2+4+6+...+50=2(1+2+3+...+25)=2 \cdot \frac{25(25+1)}{2} = \\ \\ =\not2 \cdot \frac{25 \cdot 26}{\not2} =25 \cdot 26=650$