Đáp án:

    `B=4`

Giải thích các bước giải:

 Ta có:

`B=5.((12-12/7-12/219-12/85)/(4-4/7-4/219-4/85):(5+5/13+5/169+5/91)/(6+6/13+6/169+6/91)). 158158158/711711711`

`=>B=5.((12(1-1/7-1/219-1/85))/(4(1-1/7-1/219-1/85)):(5(1+1/13+1/169+1/91))/(6(1+1/13+1/169+1/91))). 158.1001001/711.1001001`

`=>B=5.(12/4:5/6). 158/771`

`=>B=5. 18/5. 2/9=18. 2/9=4`

$B = 5[ \dfrac{12 - \dfrac{12}{7} - \dfrac{12}{289} - \dfrac{12}{85}}{4 - \dfrac{4}{7} - \dfrac{4}{289} - \dfrac{4}{85}} : \dfrac{5 + \dfrac{5}{13} + \dfrac{5}{169}+ \dfrac{5}{91}}{6 + \dfrac{6}{13} + \dfrac{6}{169}+ \dfrac{6}{91}} ]. \dfrac{158158158}{711711711}$

` ⇔B = 5.[` $\dfrac{12.(1 - \dfrac{1}{7} - \dfrac{1}{289} - \dfrac{1}{85})}{4 . (1 - \dfrac{1}{7} - \dfrac{1}{289} - \dfrac{1}{85})} : \dfrac{5 . (1 + \dfrac{1}{13} + \dfrac{1}{169} + \dfrac{1}{91})}{6 . (1 + \dfrac{1}{13} + \dfrac{1}{169} + \dfrac{1}{91})}$ `]` . $\dfrac{158}{711}$

$⇔B = 5.[ \dfrac{12}{4} : \dfrac{5}{6} ] . \dfrac{158}{711}$

`⇔B = 5. ` $\dfrac{18}{5}$ . $\dfrac{158}{711}$

$⇔B = 18 . \dfrac{158}{711}$

$⇔B =\dfrac{2844}{711}$

$⇔B =4$