51541 

`@` `\text {Ans}`

`\downarrow`

`a)`

`20 \times 6 \times 5 \times 7`

`= (6 \times 7) \times (20 \times 5)`

`= 42 \times 100`

`= 4200`

`b)`

`125 \times 789 \times 8`

`= (125 \times 8) \times 789`

`= 1000 \times 789`

`= 789000`

`c)`

`2 \times 3 \times 4 \times 8 \times 50 \times 25 \times 125`

`= (2 \times 50) \times 3 \times (4 \times 25) \times (8 \times 125)`

`= 100 \times 3 \times 100 \times 1000`

`= 300000000`

a) 20 x 6 x 5 x 7

= ( 20 x 5 ) x ( 6 x 7 )

= 100 x 42

= 4200

Ta có \(\frac{2.3.4+2.3.4.2018+2.3.4.2019-2.3.4.2020}{5.6.7+5.6.7.2018+5.6.7.2019-5.6.7.2020}\)

\(=\frac{2.3.4\left(1+2018+2019-2020\right)}{5.6.7.\left(1+2018+2019-2020\right)}=\frac{2.3.4}{5.6.7}=\frac{4}{35}\)

a: =5-7/19

=95/19-7/19

=88/19

b: =1/2(3/4+1/4)=1/2

c: =26/7(11/3-8/3)

=26/7

\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{8}{7}\times\dfrac{7}{10}\)

\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{4}{5}\)

\(x\div\dfrac{2}{3}=0\)

\(x=0\)

\(x\div\dfrac{2}{3}+\dfrac{4}{5}=\dfrac{8}{7}\cdot\dfrac{7}{10}\)

\(x\cdot\dfrac{3}{2}+\dfrac{4}{5}=\dfrac{4}{5}\)

\(x\cdot\dfrac{3}{2}=\dfrac{4}{5}-\dfrac{4}{5}=0\)

\(x=0\div\dfrac{3}{2}=0\)

Vậy x = 0

\(x\cdot\dfrac{3}{2}+\dfrac{4}{5}=\dfrac{8}{7}\cdot\dfrac{7}{10}\)

\(\dfrac{3}{2}x+\dfrac{4}{5}=\dfrac{4\cdot2\cdot7}{7\cdot2\cdot5}=\dfrac{4}{5}\)

\(\dfrac{3}{2}x=\dfrac{4}{5}-\dfrac{4}{5}=0\)

\(\Rightarrow x=0\)