Cho biểu thức: \(A = \left( {6 - \dfrac{2}{3} + \dfrac{1}{2}} \right) - \left( {5 + \dfrac{5}{3} - \dfrac{3}{2}} \right)\)\(\, - \left( {3 - \dfrac{7}{3} + \dfrac{5}{2}} \right)\)

Cách 1: Tính giá trị từng biểu thức trong ngoặc

\(\begin{array}{l}
A = \left( {6 - \dfrac{2}{3} + \dfrac{1}{2}} \right) - \left( {5 + \dfrac{5}{3} - \dfrac{3}{2}} \right) - \left( {3 - \dfrac{7}{3} + \dfrac{5}{2}} \right)\\
= \left( {\dfrac{{6.6}}{6} - \dfrac{{2.2}}{6} + \dfrac{3}{6}} \right) - \left( {\dfrac{{5.6}}{6} + \dfrac{{5.2}}{6} - \dfrac{{3.3}}{6}} \right) - \left( {\dfrac{{3.6}}{6} - \dfrac{{7.2}}{6} + \dfrac{{5.3}}{6}} \right)\\
= \dfrac{{36 - 4 + 3}}{6} - \dfrac{{30 + 10 - 9}}{6} - \dfrac{{18 - 14 + 15}}{6}\\
= \dfrac{{35}}{6} - \dfrac{{31}}{6} - \dfrac{{19}}{6} = \dfrac{{35 - 31 - 19}}{6}\\
= - \dfrac{{15}}{6} = - \dfrac{5}{2} = - 2\dfrac{1}{2}.
\end{array}\)

Cách 2: Bỏ dấu ngoặc rồi nhóm các số hạng thích hợp

\(\begin{array}{l}
A = \left( {6 - \dfrac{2}{3} + \dfrac{1}{2}} \right) - \left( {5 + \dfrac{5}{3} - \dfrac{3}{2}} \right) - \left( {3 - \dfrac{7}{3} + \dfrac{5}{2}} \right)\\
= 6 - \dfrac{2}{3} + \dfrac{1}{2} - 5 - \dfrac{5}{3} + \dfrac{3}{2} - 3 + \dfrac{7}{3} - \dfrac{5}{2}\\
= \left( {6 - 5 - 3} \right) + \left( { - \dfrac{2}{3} - \dfrac{5}{3} + \dfrac{7}{3}} \right) + \left( {\dfrac{1}{2} + \dfrac{3}{2} - \dfrac{5}{2}} \right)\\=-2 +\dfrac{-2-5+7}{3}+\dfrac{1+3-5}{2}\\
= - 2 + 0 - \dfrac{1}{2} = - \dfrac{5}{2} = - 2\dfrac{1}{2}.
\end{array}\)