Question

Aflati:
2+4+6+.......+28+30

Answer 1

$\displaystyle 2+4+6+...+28+30=2(1+2+3+...+14+15)= \\ \\ =2 \times \frac{15(15+1)}{2} =2 \times \frac{15 \times 16}{2} =\not 2 \times \frac{240}{\not 2} =240$