4bc=7cb
4(10b+c)=7(10c+b)
40b+4c=70c+7b
33b=66c
b=2c
suma numerelor este
(121+ 142+ 163+ 184)+ (221+ 242+ 263+284)+....+(921+...+984)=
=100*4+200*4+....+900*4+ 21*9+42*9+63*9+84+9=
=400(1+2+3+...+9)+ 9(21+42+63+84)=
=400*55+9*210= 220 000+1 890= 221 890
verifica, te rog, calculele
O zi buna!
