Question

1+2+3+...+100=


2+4+6+...+100=

Vă rog,repede!

Answer 1

 

$\displaystyle\bf\\1+2+3+...+100=\frac{100\times(100+1)}{2}=50\times101=5050\\\\\\2+4+6+...+100=2(1+2+3+...+50)=2\times\frac{50(50+1)}{2}=50\times51=2550$