Tính nhanh.

a) $\frac{12}{23} \times \frac{7}{13} + \frac{11}{23} \times \frac{7}{13} = \frac{7}{13} \times (\frac{12}{23} + \frac{11}{23}) = \frac{7}{13}$

b) $\frac{4}{9} \times \frac{23}{11} - \frac{1}{11} \times \frac{4}{9} + \frac{4}{9} = \frac{4}{9} \times (\frac{23}{11} - \frac{1}{11} + 1) = \frac{4}{9} \times 3 = \frac{4}{3}$

c) $[(- \frac{5}{7}) + \frac{3}{5}] / \frac{2020}{2021} + (\frac{2}{5} - \frac{2}{7}) / \frac{2020}{2021} = [(\frac{- 5}{7}) + \frac{3}{5} + \frac{2}{5} + (\frac{- 2}{7})] / \frac{2020}{2021} = 0$

d) $\frac{3}{8} / (\frac{7}{22} - \frac{2}{11}) + \frac{3}{8} / (\frac{2}{5} - \frac{1}{10}) = \frac{3}{8} / \frac{3}{22} + \frac{3}{8} / \frac{3}{10} = \frac{3}{8} \times (\frac{22}{3} + \frac{10}{3}) = 4$

Tính nhanh.

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