Răspuns :
Suma lui Gauss
11+22+33+...+198 =
= 11×(1+2+3+...+18) =
= 11 × 18 ×(18+1) : 2 =
= 11×18×19 : 2 =
= 11×19×9 =
= 1 881
11+22+33+...+198 =
= 11×(1+2+3+...+18) =
= 11 × 18 ×(18+1) : 2 =
= 11×18×19 : 2 =
= 11×19×9 =
= 1 881