Theo đề bài
\(\frac{\left(1256+5612+\overline{12ab}+\overline{ab12}+\overline{56ab}+\overline{ab56}\right)}{6}=3434\)
\(\frac{1256+5612+1200+\overline{ab}+100x\overline{ab}+12+5600+\overline{ab}+100x\overline{ab}+56}{6}=3434\)
\(202x\overline{ab}+13736=6x3434\)
\(202x\overline{ab}=6868\Rightarrow\overline{ab}=6868:202=34\)