Ok chị nha chị làm hộ em nhé

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

b> 2/3 x 3/4 x 4/5 x 5/6 = $\frac{2 x 3 x 4 x 5}{3 x 4 x 5 x 6}$  = 1/3

c>  4/5 x 3/7 + 4/5 x 4/7 = 4/5 x ( 3/7 + 4/7 ) = 4/5 x 1 = 4/5

d> 4/5 - 2/3 + 1/5 - 1/3 = ( 4/5 + 1/5 ) - ( 2/3 + 1/3 )= 1 - 1 = 0

e> 2/5 x 7/4 - 2/5 x 3/7 = 2/5 x ( 7/4 - 3/7 ) = 2/5 x 37/28 = 37/70

h> 13/4 x 2/3 x 4/13 x 3/2 = $\frac{13 x 2 x 3x 4 }{4 x 3 x 2 x 13 }$ = 1

g> 75/100 + 18/21 + 19/32 + 1/4 + 3/21 + 13/32

= 3/4 + 18/21 + 19/32 + 1/4 + 3/21 + 13/32

= ( 3/4 + 1/4 )+ ( 18/21 + 3/21 ) + ( 19/32  + 13/32 )  

=  1 + 1 + 1 

= 3

bài 2

   a> 4/7 x 5/6 + 4/6 x 1/6 = 4/7 x ( 1/6 + 5/6 ) =4/7 x 1 = 4/7

   b> 3/5 x 7/9 - 3/5 x 2/9 = 3/5 x ( 7/9 - 2/9 ) = 3/5 x 5/9 = 1/3

   c> 5/9 x 1/4 + 4/9 x 3/12 = 5/9 x 1/4 + 4/9 x 1/4 = 1/4 x ( 5/9 + 4/9 ) = 1/4 x 1                                               = 1/4

  d> 7/9 x 8/5 - 7/9 x 3/5 = 7/9 x ( 8/5 - 3/5 ) =7/9 x 1 = 7/9

  g> 2/5 x 3/4 + 3/4 x 3/5 = 3/4 x ( 2/5 + 3/5 ) = 3/4 x 1  = 3/4

 e> 2006/2005 x 3/4 - 3/4 x 1/2005 = 3/4 x 2006/2005 - 1/2005 ) = 3/4 x 1 = 3/4