Cho $M = \dfrac{{ - 5}}{{12}} - \left( {\dfrac{3}{4} + \dfrac{7}{{12}} - \dfrac{2}{8}} \right)$ và $N = \left( {\dfrac{7}{{41}} - \dfrac{4}{9}} \right) - \left( {\dfrac{3}{{19}} + \dfrac{7}{{41}}} \right) + \left( {\dfrac{4}{9} - \dfrac{{16}}{{19}}} \right)$. Chọn câu đúng.

$\begin{array}{l}M = \dfrac{{ - 5}}{{12}} - \left( {\dfrac{3}{4} + \dfrac{7}{{12}} - \dfrac{2}{8}} \right)\\ = \dfrac{{ - 5}}{{12}} - \dfrac{3}{4} - \dfrac{7}{{12}} + \dfrac{2}{8}\\ = \left( {\dfrac{{ - 5}}{{12}} - \dfrac{7}{{12}}} \right) + \left( { - \dfrac{3}{4}} \right) + \dfrac{2}{8}\\ =  - 1 - \dfrac{3}{4} + \dfrac{2}{8}\\ = \dfrac{{ - 3}}{2}\end{array}$

$\begin{array}{l}N = \left( {\dfrac{7}{{41}} - \dfrac{4}{9}} \right) - \left( {\dfrac{3}{{19}} + \dfrac{7}{{41}}} \right) + \left( {\dfrac{4}{9} - \dfrac{{16}}{{19}}} \right)\\ = \dfrac{7}{{41}} - \dfrac{4}{9} - \dfrac{3}{{19}} - \dfrac{7}{{41}} + \dfrac{4}{9} - \dfrac{{16}}{{19}}\\ = \left( {\dfrac{7}{{41}} - \dfrac{7}{{41}}} \right) + \left( { - \dfrac{4}{9} + \dfrac{4}{9}} \right) + \left( { - \dfrac{3}{{19}} - \dfrac{{16}}{{19}}} \right)\\ = 0 + 0 - 1 =  - 1\end{array}$

Vì $\dfrac{{ - 3}}{2} <  - 1$ nên $M < N$.