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Answer 1

\(Bài13\\ a,x+\dfrac{4}{5}=\dfrac{2}{3}\\ \Rightarrow x=\dfrac{2}{3}-\dfrac{4}{5}\\ \Rightarrow x=-\dfrac{2}{15}\\ ----------\\ b,x+\dfrac{3}{2}=\dfrac{11}{4}\\ \Rightarrow x=\dfrac{11}{4}-\dfrac{3}{2}\\ \Rightarrow x=\dfrac{11-3.2}{4}\\ \Rightarrow x=\dfrac{5}{4}\\ ----------\\ c,\dfrac{25}{3}-x=\dfrac{5}{6}\\ \Rightarrow x=\dfrac{25}{3}-\dfrac{5}{6}\\ \Rightarrow x=\dfrac{15}{2}\)

\(Bài14\\ a,\dfrac{12}{7}+\dfrac{19}{7}+\dfrac{18}{7}=\dfrac{12+19+18}{7}=\dfrac{49}{7}=7\\ ----------\\ b,\dfrac{2}{5}+\dfrac{7}{12}+\dfrac{13}{12}=\dfrac{2}{5}+\dfrac{5}{3}=\dfrac{2.3+5.5}{15}=\dfrac{7}{3}\)

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