Question

aflati suma numerelor care impartite la 43 dau catul 15 si restul numar par.

Answer 1

restul la impartirea cu 15 poate fi 1,2,3,4,5,6,7,8,9,10,11,12,13,14
nr pare sunt 2,4,6,8,10,12,14
nr sunt 
43×15+2=647
43×15+4=649
43×15+6=651
43×15+8=653
43×15+10=655
43×15+12=657
43×15+14=659
647+649+651+653+655+657+659=647×7+(2+4+6+8+10+12)=
=4529+2(1+2+3+4+5+6+7)=4529+2×6×7/2=4529+42=4571