a) \(\dfrac{2}{5}\cdot\dfrac{1}{7}+\dfrac{2}{5}\cdot\dfrac{5}{7}+\dfrac{2}{5}\)

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

\(=\dfrac{2}{5}\cdot\dfrac{13}{7}=\dfrac{26}{35}\)

b) \(\dfrac{1}{5}+\dfrac{2}{8}+\dfrac{4}{5}+\dfrac{7}{8}-\dfrac{1}{8}\)

\(=\left(\dfrac{1}{5}+\dfrac{4}{5}\right)+\left(\dfrac{2}{8}+\dfrac{7}{8}-\dfrac{1}{8}\right)\)

\(=1+1=2\)

c)\(\dfrac{24}{36}\cdot\dfrac{10}{12}\cdot36\)

\(=\dfrac{24\cdot10\cdot36}{36\cdot12}=\dfrac{12\cdot2\cdot10\cdot36}{12\cdot36}\)

\(=2\cdot10=20\)

a, 24/35

b, 13/7

k cho mih

120²³

tính khùng lun á bạn

=120²³

a: \(=\dfrac{3}{5}+\dfrac{2}{7}=\dfrac{21+10}{35}=\dfrac{31}{35}\)

b: \(=\dfrac{6}{5}+\dfrac{3}{2}\cdot\dfrac{1}{3}=\dfrac{6}{5}+\dfrac{1}{2}=\dfrac{12+5}{10}=\dfrac{17}{10}\)

c: \(=\dfrac{5\cdot3}{9}=\dfrac{5}{3}\)

d: =5-2/3*6/5

=5-12/15

=5-4/5

=21/5

a, 30 + 50 + 70 + 50

= ( 30 + 70 ) + ( 50 + 50 )

= 100 + 100 

= 200

b,20 + 80 + 90 + 10 

= ( 20 + 80 ) + ( 90 + 10 )

= 100 + 100

= 200

c, 3 + 5 + 5 + 7

= ( 3 + 7 ) + ( 5 + 5 )

= 10 + 10

= 20

d, 2 x 6 + 5 x 5

= 2 x 5 + 6 x 5 

= 10 + 30

= 40

30 + 50 + 70 + 50 = 200 

    còn lại làm các bạn khác

ai thấy đúng thì tk

a , 30 + 50 + 70 + 50

= ( 30 + 70 ) + ( 50 + 50 )

= 100 + 100

= 200

b , 20 + 80 + 90 + 10

= ( 20 + 80 ) + ( 90 + 10 ) 

= 100 + 100

= 200

\(\frac{3}{4}\cdot\frac{8}{5}\cdot\frac{5}{9}=\frac{2}{3}\)

\(\frac{3}{7}:\frac{3}{14}:\frac{1}{2}=4\)

cậu ghi lòi  giải ra được không

a) \(\frac{3}{4}x\frac{8}{5}x\frac{5}{9}=\frac{3x8x5}{4x5x9}=\frac{120}{180}=\frac{2}{3}\)

b) \(\frac{6}{7}:\frac{3}{14}:\frac{1}{2}=\frac{6}{7}x\frac{14}{3}x\frac{1}{2}=\frac{84}{42}=2\)

a) [ {4/5+1/5+3/10 } +1/7 ] * [3 : 6/5 ] = 13/10 * 5/2 = 13/4

b) = [1+3+5+...99] x [ 2/5 x5 - 1/2 *4 ]=[(99+1)+(98+2)+(97+3) +...+(49+51)] x  0 = 0

a) 101/28                              b)0

Mình xin lỗi nha các bạn ps1.7 là 7/10