Question

Aflati suma nr.
3 + 6 + 9 + 12 +............ + 99
5 + 10 + 15 + ...................... + 2005

Answer 1

3+6+9+.....+99=3(1+2+3+.....33)=3*(1+33)*33/2=3*34*33/2=1683


5+10+.....+2005=5(1+2+3+....+401)=5*(1+401)*401/2=403005

Answer 2

3+6+9+12+...+99=3×(1+2+3+...33)=3×$\frac{33*34}{2}$=1683
5 + 10 + 15 + ... + 2005 =5×(1+2+3+...401)=5×$\frac{401*402}{2}$=403005