Question

[Ẩn danh]

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Answer 1

[HT.Phong (9A5)]

\(1)-\left(\dfrac{3}{5}+\dfrac{3}{4}\right)-\left(\dfrac{-3}{4}+\dfrac{2}{5}\right)\\ =-\dfrac{3}{5}-\dfrac{3}{4}+\dfrac{3}{4}-\dfrac{2}{5}\\ =\left(\dfrac{3}{4}-\dfrac{3}{4}\right)+\left(-\dfrac{3}{5}-\dfrac{2}{5}\right)\\ =-1\\ 2)-\left(\dfrac{3}{7}+\dfrac{3}{8}\right)-\left(-\dfrac{3}{8}+\dfrac{4}{7}\right)\\ =-\dfrac{3}{7}-\dfrac{3}{8}+\dfrac{3}{8}-\dfrac{4}{7}\\ =\left(\dfrac{3}{8}-\dfrac{3}{8}\right)+\left(-\dfrac{3}{7}-\dfrac{4}{7}\right)\\ =-1\\ 3)\left(\dfrac{-25}{27}-\dfrac{31}{42}\right)-\left(\dfrac{-7}{27}-\dfrac{3}{42}\right)\\ =-\dfrac{25}{27}-\dfrac{31}{42}+\dfrac{7}{27}+\dfrac{3}{42}\\ =\left(\dfrac{-25}{27}+\dfrac{7}{27}\right)+\left(\dfrac{-31}{42}+\dfrac{3}{42}\right)\\ =\dfrac{-18}{27}+\dfrac{-28}{42}\\ =\dfrac{-2}{3}+\dfrac{-2}{3}\\ =-\dfrac{4}{3}\)

Answer 2

[Nguyễn Lê Phước Thịnh]

Bài 17:

4: \(\left(-\dfrac{1}{2}+\dfrac{7}{6}\right)-\left(-\dfrac{5}{2}+\dfrac{1}{6}\right)\)

\(=-\dfrac{1}{2}+\dfrac{7}{6}+\dfrac{5}{2}-\dfrac{1}{6}\)

=2-1=1

5: \(\left(\dfrac{16}{21}+\dfrac{27}{12}\right)-\left(\dfrac{14}{12}-\dfrac{5}{21}\right)\)

\(=\dfrac{16}{21}+\dfrac{27}{12}-\dfrac{14}{12}+\dfrac{5}{21}\)

\(=1-\dfrac{13}{12}=-\dfrac{1}{12}\)

6: \(\left(\dfrac{13}{23}+\dfrac{-15}{4}\right)+\left(\dfrac{10}{23}-\dfrac{1}{4}\right)\)

\(=\dfrac{13}{23}+\dfrac{10}{23}-\dfrac{15}{4}-\dfrac{1}{4}\)

\(=1-4=-3\)

Bài 18:

1: \(6\dfrac{2}{5}-\left(2\dfrac{4}{9}+4\dfrac{2}{5}\right)\)

\(=6+\dfrac{2}{5}-2-\dfrac{4}{9}-4-\dfrac{2}{5}\)

\(=-\dfrac{4}{9}\)

2: \(7\dfrac{3}{5}-\left(2\dfrac{5}{7}+5\dfrac{3}{5}\right)\)

\(=7+\dfrac{3}{5}-2-\dfrac{5}{7}-5-\dfrac{3}{5}\)

\(=-\dfrac{5}{7}\)

3: \(8\dfrac{2}{7}-\left(3\dfrac{4}{9}+4\dfrac{2}{7}\right)\)

\(=8+\dfrac{2}{7}-3-\dfrac{4}{9}-4-\dfrac{2}{7}\)

\(=1-\dfrac{4}{9}=\dfrac{5}{9}\)

4: \(8\dfrac{2}{9}-\left(4\dfrac{2}{9}-5\dfrac{1}{2}\right)\)

\(=8+\dfrac{2}{9}-4-\dfrac{2}{9}+5+\dfrac{1}{2}\)

\(=9+\dfrac{1}{2}=\dfrac{19}{2}\)

5: \(21\dfrac{4}{11}-\left(1\dfrac{3}{5}+7\dfrac{4}{11}\right)\)

\(=21+\dfrac{4}{11}-1-\dfrac{3}{5}-7-\dfrac{4}{11}\)

\(=13-\dfrac{3}{5}=\dfrac{62}{5}\)

6: \(11\dfrac{3}{13}-\left(2\dfrac{4}{7}+5\dfrac{3}{13}\right)\)

\(=11+\dfrac{3}{13}-2-\dfrac{4}{7}-5-\dfrac{3}{13}\)

\(=4-\dfrac{4}{7}=\dfrac{24}{7}\)

7: \(\left(6\dfrac{4}{9}+3\dfrac{7}{11}\right)-4\dfrac{4}{9}\)

\(=6+\dfrac{4}{9}+3+\dfrac{7}{11}-4-\dfrac{4}{9}\)

\(=5+\dfrac{7}{11}=\dfrac{62}{11}\)

8: \(\left(7\dfrac{8}{9}+2\dfrac{3}{13}\right)-4\dfrac{8}{9}\)

\(=7+\dfrac{8}{9}+2+\dfrac{3}{13}-4-\dfrac{8}{9}\)

\(=5+\dfrac{3}{13}=\dfrac{68}{13}\)

9: \(\left(6\dfrac{5}{7}+2\dfrac{7}{9}\right)-4\dfrac{5}{7}\)

\(=6+\dfrac{5}{7}+2+\dfrac{7}{9}-4-\dfrac{5}{7}\)

\(=4+\dfrac{7}{9}=\dfrac{43}{9}\)