Question

Consideram multimea A={xE N|11<sau egal x < 90}.Aflati suma elementelor lui A.
La raspuns imi da 3950

Answer 1

A = {11, 12, 13,..., 89}

11+12+...+89 =
(1+2+...+89) - (1+2+...+10) =
89*90:2 - 55 =
89*45 - 55 =
4005 - 55 = 3950