`2/5 xx 4/7 + 3/5 xx 4/7`

`= 4/7 xx (2/5 + 3/5)`

`= 4/7 xx 1`

`= 4/7`

\(\dfrac{2}{5}\times\dfrac{4}{7}+\dfrac{3}{5}\times\dfrac{4}{7}=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\times\dfrac{4}{7}=\dfrac{5}{5}\times\dfrac{4}{7}=1\times\dfrac{4}{7}=\dfrac{4}{7}\)

\(=\dfrac{4}{7}\times\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=\dfrac{4}{7}\)

1,

a,=4/7:4/9.3

=9/7.3

=27/7

b,=(7/11+4/11).5/6

=1.5/6

=5/6

`(6/7-2/7):4/9xx3=4/7xx9/4xx3=[4xx9xx3]/[7xx4]=27/7`

`7/11xx5/6+4/11xx5/6=(7/11+4/11)xx5/6=11/11xx5/6=5/6`

=3/5*\((\)2/7+4/7\()\)+2/5

=3/5*6/7+2/5

=18/35+2/5

=32/35

5/7 - 2/5 x 4/6 

= 5/7 - 2/5 x 2/3 

= 5/2 x 2/7 - 2/5 x 2/3 

= 5/2 x 2/7 + 5/2 x 2/3 

= 5/2 x 4/21

= 10/21

5/7 - 2/5 x4/6 

= 5/7 - 8/30

= 5/7 - 4/15

= (75- 28)/ 105

= 47/105

\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)

7/8 x 1/4 + 7/8 x 2/4 + 7/8

=7/8 x\(\left(\dfrac{1}{4}+\dfrac{2}{4}\right)\) + 7/8

=7/8 x 3/4 + 7/8

=7/8 x \(\left(\dfrac{3}{4}+1\right)\)

=7/8 x 7/4

=49/32

`7/8 xx 1/4 + 7/8 xx 2/4 + 7/8`

`= 7/8 xx 1/4 + 7/8 xx 2/4 + 7/8xx1`

`= 7/8 xx (1/4 +2/4+1)`

`= 7/8 xx ( 3/4 + 4/4)`

`= 7/8 xx 7/4`

`= 49/32`

` @ nkhanh`

7/8 x 1/4 + 7/8 x 2/4 + 7/8

=7/8 x 1/4 + 7/8 x 2/4 + 7/8 x 4/4

= 7/8x(1/4+2/4+4/4)

=7/8x7/4

=49/32

\(\frac{3}{4}\cdot\frac{5}{7}+\frac{5}{7}\cdot\frac{1}{4}=\left(\frac{3}{4}+\frac{1}{4}\right)\cdot\frac{5}{7}=\frac{4}{4}\cdot\frac{5}{7}=1\cdot\frac{5}{7}=\frac{5}{7}\)

(lưu ý dấu . là x nhân ý)

Chúc bạn học tốt!^_^