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Chọn đáp án: B. Các câu 1 – 2 – 4 – 6 – 8

Chọn C

Câu 1:

\(\dfrac{-5}{6}:\dfrac{3}{13}=\dfrac{-5}{6}.\dfrac{13}{3}=\dfrac{-5.13}{6.3}=\dfrac{-65}{18}\) 

Câu 2:

\(\dfrac{5}{9}:\dfrac{5}{-3}=\dfrac{5}{9}.\dfrac{-3}{5}=\dfrac{5.-3}{9.5}=\dfrac{-15}{45}=\dfrac{-1}{3}\) 

Câu 3:

\(\left(-15\right):\dfrac{3}{2}=\left(-15\right).\dfrac{2}{3}=\dfrac{-15.2}{3}=\dfrac{-30}{3}=-10\) 

Câu 4:

\(\dfrac{3}{4}:\left(-9\right)=\dfrac{3}{4}.\dfrac{-1}{9}=\dfrac{3.-1}{4.9}=\dfrac{-3}{36}=\dfrac{-1}{12}\)

Câu 1

\(-\dfrac{5}{6}:\dfrac{3}{13}=-\dfrac{5}{6}.\dfrac{13}{3}=\dfrac{-5.13}{6.3}=-\dfrac{65}{18}\)

Câu 2

\(2:\dfrac{5}{9}:\dfrac{5}{-3}=2.\dfrac{9}{5}.\dfrac{-3}{5}=\dfrac{2.9.\left(-3\right)}{5.5}=-\dfrac{54}{25}\)

Câu 3

\(4:\dfrac{3}{2}:\left(-9\right)=4.\dfrac{2}{3}.\dfrac{1}{-9}=\dfrac{4.2.1}{-9}=-\dfrac{8}{9}\)

1-C ;

2-A;

3-A;

4-C;

5-B;

6-A

C

C nha

c

Câu 1: A

Câu 2: D

Câu 3; B

Câu 4: A

Câu 5: A

Câu 1: 

\(\dfrac{2}{5}-\dfrac{1}{4}+\dfrac{3}{10}=\dfrac{8}{20}-\dfrac{5}{20}+\dfrac{6}{20}=\dfrac{8-5+6}{20}=\dfrac{9}{20}\) 

Câu 2:

\(\dfrac{-2}{5}:\left(1-\dfrac{1}{10}\right)=\dfrac{-2}{5}:\dfrac{9}{10}=\dfrac{-2}{5}.\dfrac{10}{9}=\dfrac{-2.10}{5.9}=\dfrac{-20}{45}=\dfrac{-4}{9}\) 

Câu 3:

\(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}:\dfrac{5}{14}=\dfrac{7}{18}+\dfrac{1}{5}=\dfrac{53}{90}\) 

Câu 4:

\(\dfrac{2}{7}.\dfrac{3}{11}+\dfrac{2}{7}.\dfrac{8}{11}\) 

\(=\dfrac{2}{7}.\left(\dfrac{3}{11}+\dfrac{8}{11}\right)\) 

\(=\dfrac{2}{7}.1\) 

\(=\dfrac{2}{7}\)

Câu 1

\(\dfrac{2}{5}\)-\(\dfrac{1}{4}\)+\(\dfrac{3}{10}\)= \(\dfrac{8}{20}\)-\(\dfrac{5}{20}\)+\(\dfrac{6}{20}\)=\(\dfrac{3}{20}\)+\(\dfrac{6}{20}\)=\(\dfrac{9}{20}\)

Câu 2

-\(\dfrac{2}{5}\):(1-\(\dfrac{1}{10}\))= -\(\dfrac{2}{5}\):\(\dfrac{9}{10}\)=-\(\dfrac{2}{5}\).\(\dfrac{10}{9}\)=-\(\dfrac{4}{9}\)

Câu 3

\(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}:\dfrac{5}{14}\)= \(\dfrac{7}{8}.\dfrac{4}{9}+\dfrac{1}{14}.\dfrac{14}{5}\)=\(\dfrac{7.4}{4.2.9}+\dfrac{1.14}{14.5}\)=\(\dfrac{7}{18}+\dfrac{1}{5}\)=\(\dfrac{35}{90}+\dfrac{18}{90}\)=\(\dfrac{53}{90}\)

Câu 4

\(\dfrac{2}{7}.\dfrac{3}{11}+\dfrac{2}{7}.\dfrac{8}{11}\)=\(\dfrac{2}{7}.\left(\dfrac{3}{11}+\dfrac{8}{11}\right)\)=\(\dfrac{2}{7}.1\)=\(\dfrac{2}{7}\)

Chọn đáp án: C. Cặp câu 3 – 4 và 5 – 6

Chọn B