Question

Calculeaza suma nr scrise cu cifre identice cuprinse între 10si 1000

Answer 1

11+22+33+44+55+66+77+88+99+111+222+....+999=11(1+2+3+4+5+6+7+8+9)+111(1+2+3+...+9)
S=1+2+3+4+5+6+7+8+9
S=9+8+7+6+5+4+3+2+1
2S=10+10+10+...+10 de 9 ori
S=10×9:2
S=45
11×45+111×45=5490