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 1:6/8+4/8+5/7=10/8*5/7=50/56=25/28

Cách 2 :3/4*5/7+1/2*
5/7=15/28+10/28=25/28

Cái này thầy tôi đã chữa yên tâm

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

= \(\frac{3}{4}\)

Nhào vô trả lời nhanh và đúng mk k cho!!!

nhanh! nhanh ! nhanh

có dấu ngoặc đơn ko

`(1/3 + 1/5) xx 1/4`

`= ( 5/15 + 3/15) xx 1/4`

`= 8/15 xx 1/4`

`= 8/60`

`= 2/15`

__

`(1/3 + 1/5) xx 1/4`

`= 1/3 xx 1/4 + 1/5 xx 1/4`

`= 1/12 +1/20`

`=2/15`

\(C_1:\left(\dfrac{1}{3}+\dfrac{1}{5}\right)\times\dfrac{1}{4}=\dfrac{1}{4}\times\dfrac{1}{3}+\dfrac{1}{4}\times\dfrac{1}{5}=\dfrac{1}{12}+\dfrac{1}{20}=\dfrac{2}{15}\)

\(C_2:\left(\dfrac{1}{3}+\dfrac{1}{5}\right)\times\dfrac{1}{4}=\dfrac{8}{15}\times\dfrac{1}{4}=\dfrac{8\times1}{15\times4}=\dfrac{8}{60}=\dfrac{2}{15}\)

Cách 1:

\(\left(\dfrac{1}{3}+\dfrac{1}{5}\right)\times\dfrac{1}{4}=\left(\dfrac{5}{15}+\dfrac{3}{15}\right)\times\dfrac{1}{4}=\dfrac{8}{15}\times\dfrac{1}{4}=\dfrac{8}{60}=\dfrac{2}{15}\)

Cách 2:

\(\left(\dfrac{1}{3}+\dfrac{1}{5}\right)\times\dfrac{1}{4}=\dfrac{1}{3}\times\dfrac{1}{4}+\dfrac{1}{5}\times\dfrac{1}{4}=\dfrac{1}{12}+\dfrac{1}{20}=\dfrac{5}{60}+\dfrac{3}{60}=\dfrac{8}{60}=\dfrac{2}{15}\)

1/2 + 1/3 + 1/4 + 1/5 + 4/5 + 3/4 + 2/3 + 1/2

= (1/2 + 1/2) + (1/3 + 2/3) + (1/4 + 3/4) + (1/5 + 4/5)

= 1 + 1 + 1 + 1

= 4

\(\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{4}{5}+\dfrac{3}{4}+\dfrac{2}{3}+\dfrac{1}{2}\)

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

=1+1+1+1

=4

=(12+12)+(13+23)+(14+34)+(15+45)=(12+12)+(13+23)+(14+34)+(15+45)
=(12+12)+(13+23)+(14+34)+(15+45)

=1+1+1+1

=4

1/2 + 1/3 + 1/4 + 1/5 + 4/5 + 3/4 + 2/3 + 1/2

= (1/2 + 1/2) + (1/3 + 2/3) + (1/4 + 3/4) + (1/5 + 4/5)

= 1 + 1 + 1 + 1

= 4