a) \(\dfrac{3}{8}:\dfrac{9}{4}\)

\(=\dfrac{3}{8}\times\dfrac{4}{9}\)

\(=\dfrac{3\times4}{8\times9}\)

\(=\dfrac{1\times1}{2\times3}\)

\(=\dfrac{1}{6}\)

b) \(\dfrac{8}{21}:\dfrac{4}{7}\)

\(=\dfrac{8}{21}\times\dfrac{7}{4}\)

\(=\dfrac{8\times7}{21\times4}\)

\(=\dfrac{2\times1}{3\times1}\)

\(=\dfrac{2}{3}\)

c) \(\dfrac{5}{8}:\dfrac{15}{8}\)

\(=\dfrac{5}{8}\times\dfrac{8}{15}\)

\(=\dfrac{5\times8}{8\times15}\)

\(=\dfrac{1\times1}{1\times3}\)

\(=\dfrac{1}{3}\)

a: \(=\dfrac{3}{8}\cdot\dfrac{4}{9}=\dfrac{12}{72}=\dfrac{1}{6}\)

b: \(=\dfrac{8}{21}\cdot\dfrac{7}{4}=\dfrac{56}{84}=\dfrac{2}{3}\)

c: \(=\dfrac{5}{8}\cdot\dfrac{8}{15}=\dfrac{5}{15}=\dfrac{1}{3}\)

a) \(\dfrac{5}{11}\times\dfrac{11}{6}\)

\(=\dfrac{5\times11}{11\times6}\)

\(=\dfrac{5}{6}\)

b) \(7\times\dfrac{6}{21}\)

\(=\dfrac{7\times6}{21}\)

\(=\dfrac{6}{3}\)

\(=2\)

a: \(=\dfrac{5\cdot11}{11\cdot6}=\dfrac{5}{6}\)

b: \(=7\cdot\dfrac{2}{7}=2\)

\(\frac{7}{9}+\frac{6}{7}\times\frac{4}{5}=\frac{7}{9}+\frac{24}{35}=\frac{361}{315}\)

\(\frac{21}{23}+\frac{4}{5}:\frac{6}{8}=\frac{21}{23}+\frac{16}{15}=\frac{548}{345}\)

\(\frac{5}{8}\times\frac{4}{9}:\frac{2}{3}=\frac{5}{18}:\frac{2}{3}=\frac{5}{12}\)

\(\frac{7}{12}+\frac{5}{6}-\frac{21}{24}=\frac{14}{24}+\frac{20}{24}-\frac{21}{24}=\frac{11}{24}\)

b, 

    \(\frac{21}{23}+\frac{4}{5}:\frac{6}{8}=\frac{21}{23}+\frac{4}{5}.\frac{8}{6}=\frac{21}{23}+\frac{16}{15}=1\frac{338}{345}\)

c,

    \(\frac{5}{8}.\frac{4}{9}.\frac{3}{2}=\frac{5}{12}\)

d,

    \(\frac{7}{12}+\frac{5}{6}-\frac{21}{24}=\frac{14}{24}+\frac{20}{24}-\frac{21}{24}=\frac{13}{24}\)

chán thật 

\(\dfrac{3}{4}\times\dfrac{5}{7}=\dfrac{15}{28};\dfrac{5}{8}\times\dfrac{4}{15}=\dfrac{20}{120}=\dfrac{1}{6};\dfrac{7}{12}\times\dfrac{4}{9}=\dfrac{28}{108}=\dfrac{7}{27};\)

\(\dfrac{1}{6}\times\dfrac{3}{5}=\dfrac{3}{30}=\dfrac{1}{10};\dfrac{12}{21}\times\dfrac{23}{8}=\dfrac{276}{168}=\dfrac{23}{14};\dfrac{13}{4}\times\dfrac{5}{39}=\dfrac{65}{156}=\dfrac{5}{12}\)

\(\dfrac{7}{42}\times\dfrac{13}{21}=\dfrac{91}{882}=\dfrac{13}{126};\dfrac{3}{16}\times\dfrac{4}{15}=\dfrac{12}{240}=\dfrac{1}{20}\)

2/7 / 1/7 = 10/28 = 5/14

3/8 / 9/4 = 12/72 = 2/12

8/21 / 4/7 = 56/84 = 14/21

5/8 / 15 / 8 = 1/24 / 8 = 1/192

\(a,\frac{2}{7}:\frac{4}{5}=\frac{2}{7}\times\frac{5}{4}=\frac{10}{28}=\frac{5}{14}\)

\(b,\frac{3}{8}:\frac{9}{4}=\frac{3}{8}\times\frac{4}{9}=\frac{12}{72}=\frac{1}{6}\)

\(c,\frac{8}{21}:\frac{4}{7}=\frac{8}{21}\times\frac{7}{4}=\frac{56}{84}=\frac{2}{3}\)

\(d,\frac{5}{8}:\frac{15}{8}=\frac{5}{8}\times\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

A,\(\frac{2}{7}:\frac{4}{5}=\frac{2}{7}\times\frac{5}{4}=\frac{10}{28}=\frac{5}{14}\)

B,\(\frac{3}{8}:\frac{9}{4}=\frac{3}{8}\times\frac{4}{9}=\frac{12}{72}=\frac{1}{6}\)

C.\(\frac{8}{21}:\frac{4}{7}=\frac{8}{21}\times\frac{7}{4}=\frac{56}{84}=\frac{2}{3}\)

D.\(\frac{5}{8}:\frac{15}{8}=\frac{5}{8}\times\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

Đúng 100%

a, \(\frac{2}{7}:\frac{4}{5}=\)\(\frac{2}{7}x\)\(\frac{5}{4}\)\(\frac{10}{28}=\frac{5}{14}\)

b,\(\frac{3}{8}:\frac{9}{4}\)\(=\frac{3}{8}x\)\(\frac{4}{9}\)\(=\frac{12}{72}=\frac{1}{6}\)

c,\(\frac{8}{21}:\frac{4}{7}\)\(=\frac{8}{21}x\)\(\frac{7}{4}\)\(=\frac{56}{84}=\frac{2}{3}\)

d,\(\frac{5}{8}:\frac{15}{8}\)\(\frac{5}{8}x\)\(\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

tk giup mk nha

a: \(\dfrac{x}{0.9}=\dfrac{5}{6}\)

\(\Leftrightarrow x=\dfrac{3}{4}\)

b: \(\dfrac{-6}{x}=\dfrac{9}{-15}\)

\(\Leftrightarrow x=10\)

c: \(\dfrac{\dfrac{14}{15}}{\dfrac{9}{10}}=\dfrac{x}{\dfrac{3}{7}}\)

\(\Leftrightarrow x=\dfrac{3}{7}\cdot\dfrac{14}{15}:\dfrac{9}{10}=\dfrac{2}{5}\cdot\dfrac{10}{9}=\dfrac{20}{45}=\dfrac{4}{9}\)

\(\frac{5}{7}-\frac{4}{17}=\frac{5}{7}-\frac{2}{8,5}=\frac{42,5}{59,5}-\frac{14}{59,5}=\frac{38,5}{59,5}\)

\(\frac{21}{27}-\frac{2}{9}=\frac{7}{9}-\frac{2}{9}=\frac{5}{9}\)

\(\frac{13}{5}-\frac{35}{25}=\frac{13}{5}-\frac{7}{5}=\frac{6}{5}\)

chắc ko hả bạn vip à nghi quá chắc ko được đâu