Các số được lập từ a, b, c là:\(\overline{abc};\overline{acb};\overline{bac};\overline{bca};\overline{cab};\overline{cba}\)
\(\overline{abc}+\overline{acb}+\overline{bac}+\overline{bca}+\overline{cab}+\overline{cba}\\ =\left(100a+10b+c\right)+\left(100a+10c+b\right)+\left(100b+10a+c\right)+\left(100b+10c+a\right)+\left(100c+10a+b\right)+\left(100c+10b+a\right)\\ =100a+10b+c+100a+10c+b+100b+10a+c+100b+10c+a+100c+10a+b+100c+10b+a\\ =100\left(a+b+c+a+b+c\right)+10\left(a+b+c+a+b+c\right)+\left(a+b+c+a+b+c\right)\\ =100\cdot\left(15+15\right)+10\left(15+15\right)+\left(15+15\right)\\ =\left(100+10+1\right)\left(15+15\right)\\ =111\cdot30\\ =3330\)
