Question

calculati suma tuturor numere naturale de trei cifre,care impartite la 31 dau rest 13.

Answer 1

100<31×x+13<999
x={3,4,5......31}
nr de termeni  31-3+1=29
S=31×(3+4+5+...+31)+13×29=31(1+2+3+4+5+...+31-1-2)+377=
=31×(31×32/2-6)+377=31×(31×16-3)+377=31×490+377=15660