\(\dfrac{2}{7}\cdot\dfrac{2}{11}+\dfrac{5}{7}\cdot\dfrac{12}{11}-\dfrac{5}{7}\cdot\dfrac{7}{11}\)
\(=\dfrac{4}{77}+\dfrac{5}{7}\left(\dfrac{12}{11}-\dfrac{7}{11}\right)\)
\(=\dfrac{4}{77}+\dfrac{5}{7}\cdot\dfrac{5}{11}=\dfrac{4}{77}+\dfrac{25}{77}=\dfrac{29}{77}\)
p/s: toán 6