A, 3/4 + -6/7 + 9/14 B, 1/3 – -1/4 – 5/12

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1. A, 3/4 + -6/7 + 9/14

   ⇒ $\frac{21}{28}$ + $\frac{-24}{28}$ + $\frac{18}{28}$ 

    = $\frac{15}{28}$ 

   B, 1/3 – -1/4 – 5/12

   ⇒ $\frac{4}{12}$ + $\frac{3}{12}$  – $\frac{5}{12}$ 

   = $\frac{7}{12}$ – $\frac{5}{12}$

   =$\frac{2}{12}$ = $\frac{1}{6}$  

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2. Đáp án:

    A, $\frac{3}{4}+\frac{-6}{7}+\frac{9}{14}$ 

        $=\frac{3×7}{28}+\frac{-6×4}{28}+\frac{9×2}{28}$

        $=\frac{21-24+18}{28}=\frac{15}{28}$

   B, $\frac{1}{3}-\frac{-1}{4}-\frac{5}{12}$

       $=\frac{1×4}{12}+\frac{1×3}{12}-\frac{5}{12}$

       $=\frac{4+3-5}{12}=\frac{2}{12}=\frac{1}{6}$

   #NOCOPY

    

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