a) 1/2 : x - 5/6 = -2/3
1/2 : x = -2/3 + 5/6
1/2 : x = -4/6 + 5/6
1/2 : x = 1/6
x = 1/2: 1/6
x = 3
b) 20% . x + 5/8 - x . 0,5 = 11/20
1/5 . x + 5/8 - x . 1/2 = 11/20
x . (1/5 + 5/8) - 1/2 = 11/20
x . 33/40 - 1/2 = 11/20
x . 13/40 = 11/20
x = 11/20 : 13/40
x = 22/13
c) chịu