Question

Aflati cat numere de trei cifre impartite la 21 dau restul 12.
Aflati suma tuturor numerelor naturale de trei cifre care impartite la 21 dau restul 12.

Answer 1

primul nr. de 3 cifre :21 care da rest 12...este 117

117:21=5,57 => 117=21*5+12...adica 105+12=117
117:21=5 rest 12

urmatoarele numere sunt:159;201;243;285;327;369;411;453;495;537;579;621;663;705;;747;789;831;873;915;957;999.

159:21=7 rest 12 =>7*21+12=147+12=159
201:21=9 rest 12 =>9*21+12=189+12=201
243:21=11 rest 12
285:21=13 rest 12
327:21=15 rest 12
369:21=17 rest 12
411:21=19 rest 12
453:21=21 rest 12
495:21=23 rest 12
537:21=25 rest 12
579:21=27 rest 12
621:21=29 rest 12=> 21*29+12=609+12=621
663:21=31 rest 12
705:21=33 rest 12
747:21=35 rest 12
789:21=37 rest 12
831:21=39 rest 12=>21*39+12=819+12=831
873:21=41 rest 12
915:21=43 rest 12
957:21=45 rest 12
999:21=47 rest 12=>21*47+12=987+12=999