To simplify this expression, we first need to find the values of sin, cos, ctg, and tg for the given angles:

sin(30°) = 0.5
cos(60°) = 0.5
ctg(45°) = 1
tg(180°) = 0

Now we substitute these values into the expression:

sin(30°) - 2cos(60°) + ctg(45°) - tg(180°)
= 0.5 - 2(0.5) + 1 - 0
= 0.5 - 1 + 1
= 0.5

Therefore, sin(30°) - 2cos(60°) + ctg(45°) - tg(180°) simplifies to 0.5.