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Calculati suma tuturor nr de forma 3ab.

Răspuns :

S=300+301+...+399=

=300+(300+1)+...+(300+99)=

=300x100+(1+2+...+99)=30000+99x100/2=30000+4950=34950
300+301+302+ ...+399 =
= 300+300+1+300+2+...300+99
= 300 x 100 + 99 x 100:2
= 30.000 + 99 x 50
= 30.000 + 4950
= 34950