Question

S= 10+20+30+...+100
Va rog ajutati-ma...!!!!

Answer 1

S=10+100+20+90+30+80+....=110+110+110+...+110=110*5=550

Answer 2

$\displaystyle 10+20+30+...+100=10(1+2+3+...+10)=10 \times \frac{10(10+1)}{2}= \\ \\ =10 \times \frac{10 \times 11}{2} =10 \times \frac{110}{2} =10 \times 55=550$