Question

1+2+3+...+2005-1001-1002-...-2006 cel mai rapid coroana

Answer 1

( 1 +2+ 3 + .. + 2005)   -  ( 1001 + 1002 + ... + 2006) = 
 suma  de 2005 termeni             suma de 1006 termeni 
= ( 1 + 2005 ) ·2005 / 2   - ( 1001 + 2006 ) ·1006 /2 = 
= 2006 · 2005 :2    - 3007 · 503 =
 = 1003 · 2005  - 3007 ·503 = 
 = 2011015 -1512521=498494

Answer 2

(1+2005)×2005÷2=
2006×2005÷2=
4022030÷2=2011015
2006-1001+1=1006nr
(2006+1001)×1006÷2=
3007×1006÷2=
3025042÷2=1512521
2011015-1512521=499494