3/5 x 8/27 x 5/3= 3/5 x 5/3 x 8/27= 8/27

7/19 x 1/3 + 7/19 x 2/3 = 7/19 x (1/3 + 2/3)= 7/19 x 1 = 7/19

3/5 x 8/27 x 5/3=8/27 vì 3/5 x 5/3 =1 

tương tự : 7/9x1/3x7/9x2/3=1/3x2/3=2/9

= 3/2 x (4/7 + 3/7)

= 3/2 x   1

= 3/2

3/2 x ( 4/7 + 3/7 )

= 3/2 x 1

= 3/2

\(\dfrac{3}{2}\times\dfrac{4}{7}+\dfrac{3}{7}\times\dfrac{3}{2}\\ =\dfrac{3}{7}\times\dfrac{4}{2}+\dfrac{3}{7}\times\dfrac{3}{2}\\ =\dfrac{3}{7}\times\left(\dfrac{4}{2}+\dfrac{3}{2}\right)\\ =\dfrac{3}{7}\times\dfrac{7}{2}\\ =\dfrac{3}{2}\)

a) \(19\times\left(52+38\right)-9\times\left(52+38\right)=\)

\(=\)     \(19\times90-9\times90\) 

\(=90\times\left(19-9\right)\) 

\(=90\times10\) 

\(=900\) 

b) \(\dfrac{2}{5}\div\dfrac{3}{7}\times\dfrac{3}{7}\div\dfrac{2}{5}+2019=\)

\(=\left(\dfrac{2}{5}\div\dfrac{2}{5}\right)\times\left(\dfrac{3}{7}\div\dfrac{3}{7}\right)+2019\) 

\(=1\times1+2019\) 

\(=2019\)

\(\left(a\right)\frac{3}{5}\cdot\frac{8}{21}\cdot\frac{5}{3}=\left(\frac{3}{5}\cdot\frac{5}{3}\right)\cdot\frac{8}{21}=1\cdot\frac{8}{21}=\frac{8}{21}\)

(b) sai đề

\(\left(c\right)x\cdot\frac{1}{2}=\frac{1}{3}\)

\(x=\frac{\frac{1}{3}}{\frac{1}{2}}=\frac{2}{3}\)

\(\left(d\right)\frac{x}{\frac{4}{5}}=\frac{5}{2}\)

\(x=\frac{5}{2}\cdot\frac{4}{5}=2\)

\(\left(e\right)\frac{\frac{2}{9}}{x}=\frac{2}{3}\)

\(x=\frac{\frac{2}{9}}{\frac{2}{3}}=\frac{1}{3}\)

\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)

5

\(\dfrac{7}{19}\times\dfrac{1}{3}+\dfrac{7}{13}\times\dfrac{2}{3}\)

\(=\dfrac{7}{19}\times\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)

\(=\dfrac{7}{19}\times1\)

\(=\dfrac{7}{19}\)

giải chi tiết hộ mình nhé

\(3\times\dfrac{7}{10}+\dfrac{7}{10}\times5+2\times\dfrac{7}{10}\)

\(=\dfrac{7}{10}\times\left(3+5+2\right)\)

\(=\dfrac{7}{10}\times10\)

\(=\dfrac{70}{10}=7\)

giúp mình đi T.T

19 x ( 52 + 38 ) - 9 x ( 52 + 38 )

= 19 x 90 - 9 x 90

= ( 19 - 9 ) x 90

= 10 x 90

= 900

\(\dfrac{2}{5}:\dfrac{3}{7}\times\dfrac{3}{7}:\dfrac{2}{5}+2019=\left(\dfrac{2}{5}:\dfrac{2}{5}\right)\times\left(\dfrac{3}{7}:\dfrac{3}{7}\right)+2019=1\times1+2019=1+2019=2020\)