tính một cách hợp lí: B=-5/7+8/11+(-2/7)+1/2+(3/11+8/11)

$\text{B = $\dfrac{-5}{7}$ + $\dfrac{8}{11}$ + $\dfrac{-2}{7}$ + $\dfrac{1}{2}$ + ( $\dfrac{3}{11}$ + $\dfrac{8}{11}$}$

$\text{B = ( $\dfrac{-5}{7}$ + $\dfrac{-2}{7}$ ) + $\dfrac{8}{11}$ + $\dfrac{1}{2}$ + ( $\dfrac{3}{11}$ + $\dfrac{8}{11}$ )}$                     

$\text{B = $\dfrac{-7}{7}$ + $\dfrac{8}{11}$ + $\dfrac{1}{2}$ + $\dfrac{11}{11}$}$

$\text{B = ( -1 ) + $\dfrac{8}{11}$ + $\dfrac{1}{2}$ + 1}$

$\text{B = [ ( -1 ) + 1 ] + $\dfrac{8}{11}$ + $\dfrac{1}{2}$}$

$\text{B = 0 + $\dfrac{8}{11}$ + $\dfrac{1}{2}$}$

$\text{B = $\dfrac{16}{22}$ + $\dfrac{11}{22}$}$

$\text{B = $\dfrac{16 + 11}{22}$}$

$\text{B = $\dfrac{27}{22}$}$

Vậy $\text{B = $\dfrac{27}{22}$}$