`\overline{1a26} + \overline{4b4}+ \overline{57c} ? \overline{abc} + 2000`
Ta có : `\overline{1a26} + \overline{4b4}+ \overline{57c} = 1000 + 100a + 20 + 6 + 400 + 10b + 4+ 500 + 70 + c = (1000 + 20 + 6 + 4 + 400 + 500 + 70) + ( 100a + 10b + c ) = 2000 + \overline{abc}`
Vì` 2000 + \overline{abc} = 2000 + \overline{abc}` nên` \overline{1a26} + \overline{4b4}+ \overline{57c} = \overline{abc} + 2000`
