cách 1:(3/4*1/2)*2

= 3/8*2

=6/8

=2/4

=2

C1 : 3/4 x 1/2 x 2

= 3/8 x 2

= 3/4

C2 : 3/4 x 1/2 x 2

= 3/4 x ( 1/2 x 2 )

= 3/4 x 1

= 3/4

a) Cách 1 : (3/4 + 1/2) x 5/7

               = 5/4 x 5/7

                = 25/28

Cách 2 : (3/4 + 1/2) x 5/7

           = 3/4 x 5/7 + 1/2 x 5/7

            = 15/28 + 5/14

            = 25/28

b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21

= 65/147 + 26/147

= 13/21

Cách 2 : 5/7 x 13/21 + 2/7 x 13/21

= (5/7 + 2/7) x 13/21

= 1 x 13/21

= 13/21

câu c tự làm

8 /15 :2/3+7/15:2/3 =                                              tính bằng 2 cách nhé các bạn

cách 1 tính sai:  3x4 =12 bằng 20 là sai r

Cách 1

\(\left(\frac{2}{3}-\frac{1}{4}\right)\cdot\frac{1}{2}=\left(\frac{8}{12}-\frac{3}{12}\right)\cdot\frac{1}{2}=\frac{5}{12}\cdot\frac{1}{2}=\frac{5}{24}\)

Cách 2\(\left(\frac{2}{3}-\frac{1}{4}\right)\cdot\frac{1}{2}=\frac{2}{3}\cdot\frac{1}{2}-\frac{1}{4}\cdot\frac{1}{2}=\frac{1}{3}-\frac{1}{8}=\frac{8}{24}-\frac{3}{24}=\frac{5}{24}\)

Cách 1 : (2/3 - 1/4) x 1/2

           = 5/12 x 1/2

           = 5/24

Cách 2 : (2/3 - 1/4) x 1/2

           = 2/3 x 1/2 - 1/4 x 1/2

           = 1/3 - 1/8

           = 5/24

kb vs tớ nha

  \(\dfrac{3}{4}\cdot\dfrac{2}{5}-\dfrac{3}{4}\cdot\dfrac{2}{7}\)

= \(\dfrac{3}{4}\cdot\left(\dfrac{2}{5}-\dfrac{2}{7}\right)\)

= \(\dfrac{3}{4}\cdot\left(\dfrac{14}{35}-\dfrac{10}{35}\right)\)

= \(\dfrac{3}{4}\cdot\dfrac{4}{35}\)

= \(\dfrac{3}{35}\)

Bài làm :

\(a,\frac{1}{7}+\frac{3}{4}+\frac{2}{7}+\frac{4}{7}\)

\(=\left(\frac{1}{7}+\frac{2}{7}+\frac{4}{7}\right)+\frac{3}{4}\)

\(=1+\frac{3}{4}\)

\(=\frac{7}{4}\)

\(b,\frac{4}{7}:\frac{2}{5}+\frac{3}{7}:\frac{2}{5}-\frac{7}{9}\)

\(=\left(\frac{4}{7}+\frac{3}{7}\right):\frac{2}{5}-\frac{7}{9}\)

\(=1:\frac{2}{5}-\frac{7}{9}\)

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

\(=\frac{31}{18}\)

Học tốt

\(a,\frac{1}{7}+\frac{3}{4}+\frac{2}{7}+\frac{4}{7}\)

\(=\left(\frac{1}{7}+\frac{2}{7}+\frac{4}{7}\right)+\frac{3}{4}\)

\(=1+\frac{3}{4}\)

\(=\frac{7}{4}\)

\(b,\frac{4}{7}:\frac{2}{5}+\frac{3}{7}:\frac{2}{5}-\frac{7}{9}\)

\(=\left(\frac{4}{7}+\frac{3}{7}\right):\frac{2}{5}-\frac{7}{9}\)

\(=1:\frac{2}{5}-\frac{7}{9}\)

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

\(=\frac{31}{18}\)

a) Cách 1

\(\frac{3}{4}\)x \(\frac{1}{2}\)x \(2\)

= \(\frac{3}{8}\)x \(2\)

= \(\frac{3}{4}\)

Cách 2

\(\frac{3}{4}\)x \(\frac{1}{2}\)x \(2\)

= \(\frac{3}{4}\)x \(\left(\frac{1}{2}x2\right)\)

= \(\frac{3}{4}\)x 1

= \(\frac{3}{4}\)