A) 3/5+-1/3 B) -2/13+-11/26 C) -2+-5/8 D)13/30-1/5 E) 2/21+-1/28

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1. Đáp án:

   \(a,\ \dfrac{4}{15}\\ b,\ \dfrac{-15}{26}\\ c,\ \dfrac{-21}{8}\\ d,\ \dfrac{7}{30}\\ e,\ \dfrac{5}{84}\)

   Giải thích các bước giải:

   \(a,\ \dfrac{3}{5}+\left (\dfrac{-1}{3} \right )=\dfrac{3.3}{5.3}+\dfrac{(-1).5}{3.5}=\dfrac{9}{15}+\dfrac{-5}{15}=\dfrac{4}{15}\\ b,\ \left (\dfrac{-2}{13} \right )+\left (\dfrac{-11}{26} \right )=\left (\dfrac{-2.2}{13.2} \right )+\left (\dfrac{-11}{26} \right )=\left (\dfrac{-4}{26} \right )+\left (\dfrac{-11}{26} \right )=\dfrac{-15}{26}\\ c,\ (-2)+\left (\dfrac{-5}{8} \right )=\left (\dfrac{-2.8}{8} \right )+\left (\dfrac{-5}{8} \right )=\left (\dfrac{-16}{8} \right )+\left (\dfrac{-5}{8} \right )=\dfrac{-21}{8}\\ d,\ \dfrac{13}{30}-\dfrac{1}{5}=\dfrac{13}{30}-\left (\dfrac{1.6}{5.6} \right )=\dfrac{13}{30}-\dfrac{6}{30}=\dfrac{7}{30}\\ e,\ \dfrac{2}{21}+\left (\dfrac{-1}{28} \right )=\left (\dfrac{2.4}{21.4} \right )+\left (\dfrac{-1.3}{28.3} \right )=\dfrac{8}{84}+\left (\dfrac{-3}{84} \right )=\dfrac{5}{84}\)

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2. Đáp án:

    

   Giải thích các bước giải:

    a) 3/5 + (-1/3)

   =9/15 + (-5/15)

   =4/15

   b)(-2/13) + (-11/26)

   =(-4/26) + (-11/26)

   =-15/26

   c)(-2) + (-5/8)

   =(-16/8) + (-5/8)

   =-21/8

   d)13/30 – 1/5

   =13/30 – 6/30

   =7/30

   e)2/21 + (-1/28)

   =8/64 + (-3/64)

   =-21/64

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