\(\dfrac{3}{4}.\dfrac{2}{3}-\dfrac{1}{6}.\dfrac{3}{4}-\dfrac{3}{4}.\dfrac{1}{2}\) 

= \(\dfrac{3}{4}.\left(\dfrac{2}{3}-\dfrac{1}{6}-\dfrac{1}{2}\right)\) 

= \(\dfrac{3}{4}.0\) 

= 0

\(\dfrac{3}{4}\cdot\dfrac{2}{3}-\dfrac{1}{6}\cdot\dfrac{3}{4}-\dfrac{3}{4}\cdot\dfrac{1}{2}\)

\(=\dfrac{3}{4}\left(\dfrac{2}{3}-\dfrac{1}{6}-\dfrac{1}{2}\right)\)

\(=\dfrac{3}{4}\cdot\left(\dfrac{4}{6}-\dfrac{1}{6}-\dfrac{3}{6}\right)\)

=0

7

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

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

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

^_\(=7\)

\(3\times\dfrac{7}{10}+\dfrac{7}{10}\times5+2\times\dfrac{7}{10}=\dfrac{7}{10}\left(3+5+2\right)=\dfrac{7}{10}\times10=7\)

= 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

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

`3+1/9+3/9+2+5/9+3+2`

`= ( 3 +2+3+2) +(1/9+ 3/9 + 5/9)`

`= 10 + 9/9`

`=10 + 1`

`=11`

\(3+\dfrac{1}{9}+\dfrac{3}{9}+2+\dfrac{5}{9}+3+2\)

\(=3+\left(\dfrac{1}{9}+\dfrac{3}{9}+\dfrac{5}{9}\right)+2+3+2\)

\(=\left(3+2+3+2\right)+\dfrac{9}{9}\)

\(=10+1=11\)

18 phần11 nhân4 phần5 trừ7 phần11 nhân4 phần5 cộng9 phần3 nhân2 phần5

a)

C1: 4✖5✖3                           C2:4✖5✖3          

=20✖3                                   =12✖5

=60                                         =60

b)

C1: 3✖5✖6                         C2:3✖5✖6      

=15✖6                                  =18✖5

=90                                        =90

Tính thuận tiện

a)13✖5✖2                         b)5✖2✖34

=13✖10                              =10✖34

=130                                   =340

tính bằng 2 cách:
a.4 nhân 5 nhân 3

C1 : 4 x 5 x 3

 = 20 x 3

 = 60

C2 : 4 x 5 x 3

= ( 4 x 5 ) x 3

= 20 x 3

= 60
b.3 nhân 5 nhân 6

C1 : 3 x 5 x 6

= 15 x 6

= 90

C2 : 3 x 5 x 6

= 3 x ( 5 x 6 )

= 3 x 30

= 90
tính bằng cách thuận tiện nhất:
a.13 nhân 5 nhân 2

13 x 5 x 2

= 13 x ( 5 x 2 )

= 13 x 10

= 130
b.5 nhân 2 nhân 34

5 x 2 x 34

= ( 5 x 2 ) x 34

= 10 x 34

= 340

812 x 5 + 812 x 7 - 7 - 812 x 2 ???

 toàn câu hỏi sai

=1500

\(2\times3\times4\times5\\ =\left(2\times5\right)\times\left(3\times4\right)\\ =10\times12=120\)

`a) 5 / 13 xx 4 / 15 xx 13 = [ 5 xx 4 xx 13 ] / [ 13 xx 5 xx 3 ] = 4 / 3`

`b) ( 3 / 7 + 5 / 2 ) xx 7 / 5 = 3 / 7 xx 7 / 5 + 5 / 2 xx 7 / 5 = 3 / 5 + 7 / 2 = 6 / 10 + 35 / 10 = 41 / 10`

`c) 1 / 5 xx 11 / 18 + 11 / 18 xx 3 / 5 = 11 / 18 xx ( 1 / 5 + 3 / 5 ) = 11 / 18 xx 4 / 5 = [ 11 xx 2 xx 2 ] / [ 2 xx 9 xx 5 ] = 22 / 45`

\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{4}{3}\)

\(b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\left(\dfrac{6}{14}+\dfrac{35}{14}\right)\times\dfrac{7}{5}=\dfrac{41}{14}\times\dfrac{7}{15}=\dfrac{41}{30}\)

\(c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)