BT2: Tính nhanh

5) \(\dfrac{1}{7}.\dfrac{2}{5}+\dfrac{1}{7}.\dfrac{1}{5}+\dfrac{1}{7}.\dfrac{4}{5}\)

6) \(\dfrac{-3}{7}.\dfrac{19}{11}+\dfrac{-2}{7}.\dfrac{3}{11}+4\dfrac{6}{11}\)

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