Bài 1:
a) x + (-3)/10 = 7/15  - 4/5
x + -3/10 = 7/15 - 12/15
x + -3/10 = -5/15
x = -5/15 + 3/10 
x= -10/30 + 9/30 
x = -1/30
vậy x = -1/30 
b) (-3)/4 + x = 5/6 + (-5/8) 
x = 5/6 + (-5/8) + 3/4
x = 40/48 - 30/48  + 36/48
x = 46/48
x = 23/24
vậy x = 23/24
c)  -3/5 - x= 3/5 - 1/2 
-3/5 - x = 6/10 - 5/10
-3/5 - x = 1/10
x = -3/5 - 1/10
x = -6/10 - 1/10
x = -7/10 
Vậy x = -7/10     
d) x + 5/6 = 1/4 + (-3/5)
x + 5/6 = 5/20 - 12/20
x + 5/6 = (-7/20)
x = (-7/20) - 5/6
x = (-42/ 120) - 100/120 
x = -142/120
x = 71/ 60
Vậy x = 71/60
e) (-1/2) - x  = (-3/4) - 5/6
(-1/2) - x = (-18/24) - 20/24
(-1/2) - x = -38/24
x = (-1/2) - (-19/12)
x = (-6/12) + 19/12
x = 13 /12
Vậy x = 13/12
Bài 2:a) -4/5 + 2/7 - 1/5 - 9/7
= (-4/5 - 1/5 ) + (2/7 -  9/7 )
= -5/5 + (-7/7)
= -1 + -1
= -2
b)  1/12 -( 1/2 + 7/12)
= 1/12 - 1/2 - 7/12
= -6/12 - 1/2
= -1/2 - 1/2 = -2 /2= -1
c) -12/5 -  (3/5 - 1/8)
= -12/5 - 3/5 + 1/8
= -15/5 + 1/8
= -3 + 1/8 
= -24/8 + 1/8 
= -23/8