Tính nhanh -2/5+3/-4+6/7+3/4+2/5

Các bn ơi giúp mk vs nha mấy bn!!

Câu 1: Tìm x, biết

a, x = \(\dfrac{1}{4}\) + \(\dfrac{2}{13}\)

b, \(\dfrac{x}{3}\) = \(\dfrac{2}{3}\) + \(\dfrac{-1}{7}\) +

Câu 3: Tính nhanh:

a, \(\dfrac{-2}{5}\) +\(\dfrac{3}{-4}\) + \(\dfrac{6}{7}\) + \(\dfrac{3}{4}\) + \(\dfrac{2}{5}\)

b, \(\dfrac{7}{15}\) + \(\dfrac{4}{-9}\) + \(\dfrac{-2}{11}\) + \(\dfrac{8}{15}\) + \(\dfrac{-5}{9}\)

c, \(\dfrac{-5}{7}\) + \(\dfrac{5}{13}\) +\(\dfrac{-20}{41}\) + \(\dfrac{8}{13}\) + \(\dfrac{-21}{41}\)

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