Ta có `: overline{abc} xx 9 = overline{1abc}`
`overline{abc} xx 9 = 1000 + overline{abc}`
`overline{abc} xx 9 - overline{abc} = 1000`
`overline{abc} xx ( 9 - 1 ) = 1000`
`overline{abc} xx 8 = 1000`
`overline{abc} = 1000 : 8`
`overline{abc} = 125`
Vậy `; a = 1 , b = 2 , c = 5 .`
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Ta có `: overline{ab} + 774 = overline{ab0}`
`overline{ab} + 774 = overline{ab} xx 10`
`overline{ab} xx 10 - overline{ab} = 774`
`overline{ab} xx ( 10 - 1 ) = 774`
`overline{ab} xx 9 = 774`
`overline{ab} = 774 : 9`
`overline{ab} = 86`
Vậy `; a = 8 , b = 6 .`
