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a fost răspuns

calculati suma numerelor mai mici decat 500 care contin cifra 3 de exact 3 de exact doua ori

Răspuns :

Emy78
cifra 3 de exact 2 ori
33+133+233+433+303+313+323+343+353+363+373+383+393+330+331+332+334+335+336+337+338+339=
(33+100+33+200+33+400+33)+18×300+ (3+13+23+43+53+63+73+83+93+30+31+32+34+35+36+37+38+39)=
632+5400+(3+10+3+20+3+40+3+50+3+60+3+70+3+80+3+90+3)+(30+30+1+30+2+30+4+30+5+30+6+30+7+30+8+30+9)=
6032+(9×3+420)+(9×30+42)=
6032+447+312=6791