B=$\frac{x}{y}$ - $\frac{1}{4}$ + $\frac{5}{8}$ - $\frac{7}{13}$/$\frac{2}{12}$ + $\frac{10}{24}$ - $\frac{14}{39}$

B=$\frac{5}{6}$/$\frac{-10}{11}$ - $\frac{3}{12}$ + $\frac{15}{24}$ - $\frac{21}{39}$/$\frac{2}{12}$ + $\frac{10}{24}$ - $\frac{14}{39}$

B=$\frac{5}{6}$/$\frac{-10}{11}$ - 3.($\frac{1}{12}$ + $\frac{5}{24}$ - $\frac{7}{39}$/$\frac{1}{12}$ + $\frac{5}{24}$ - $\frac{7}{39}$)

B=$\frac{5}{6}$/$\frac{-10}{11}$ - $\frac{3}{2}$

B=$\frac{5}{6}$ ÷ $\frac{-10}{11}$ - $\frac{3}{2}$

B=$\frac{5}{6}$ × $\frac{-10}{11}$ - $\frac{3}{2}$

B=$\frac{-11}{12}$ - $\frac{3}{2}$

B=$\frac{-11}{12}$ - $\frac{18}{12}$

B=$\frac{-29}{12}$

Mấy bài này cho nhìu điểm tí nha

Vs `x=5/6;y=-10/11` thì `x : y = x/y=5/6  : (-10/11)= -5/6.    11/10 = -11/12`

`=> B = -11/12 + (1/4+5/8-7/13) / (-2/12-10/24+14/39)` 

`=> B = -11/12 + (1/4+5/8-7/13)/((-2/3)(1/4+5/8-7/13))`

`=> B =- 11/12 -2/3 = -11/12-8/12=-19/12`