Question

Calculati: 3+5+7+9+...+2005-2-4-6-8-...-2004

Answer 1

3+5+7+9+...+2005-(2+4+6+8+...+2004)=
(2*1+1)+(2*2+1)+(2*3+1)+...+(2*1002+1)-2(1+2+3+...+1002)=
2(1+2+3+...+1002)+1*1002-2(1+2+3+...1002)=
1*1002=1002

Answer 2

 3 + 5 + 7 + 9 + ... + 2005 din care scadem
-2 -  4  - 6 - 8  - ...  - 2004        (2004:2=1002 termeni )
 1 + 1  +1 + 1 + ...  +     1  = 1 * 1002 = 1002