abc2 - 2abc = 2142
<=> abc*10+2 - 2000 -abc = 2142
<=> abc*10-abc = 2142+2000 - 2
<=> abc*9 =4140
<=> abc = 460
Vậy abc = 460
=>(abc*10+2)-(2000+abc)=2142
=>(abc*10-abc)-(2000-2)=2142
=>abc*9-1998=2142
=>abc*9=2142+1998
=>abc*9=4140
=>abc=4140:9
=>abc=460
=>(abc*10+2)-(2000+abc)=2142
=>(abc*10-abc)-(2000-2)=2142
=>abc*9-1998=2142
=>abc*9=2142+1998
=>abc*9=4140
=>abc=4140:9
=>abc=460
=>(abc*10+2)-(2000+abc)=2142
=>(abc*10-abc)-(2000-2)=2142
=>abc*9-1998=2142
=>abc*9=2142+1998
=>abc*9=4140
=>abc=4140:9
=>abc=460
460. Không ai tin thử lại mà xem . 468 là sai