Question

Calculati cate numere naturale de cel mult trei cifre impartite la 30 dau restul 7 si apoi calculati  suma acestor numere .

Answer 1

abc:30 =c rest 7 ⇒ abc=30c+7
100 < 30c+7< 999
93< 30c < 992
93/30 < c< 992/30
3,1<c<33,06
c∈{4,5,6,.....33}
Sunt 30 de numere care respecta cerinta
S=(30*4+7)+(30*5+7)+.......+(30*33+7)=30(4+5+...+33)+30*7=30*(4+33)*30/2+30*7=
30*37*15+30*7=30(37*15+7)=30*562=16860