To simplify this expression, we will first write the values of sine and cosine of the given angles:

sin(50°) = 0.766
cos(320°) = -0.766
sin(25°) = 0.422
cos(25°) = 0.906

Now, we can substitute these values into the expression and simplify:

sin(50°) - cos(320°) / 2 sin(25°) cos(25°)
= 0.766 - (-0.766) / 2 0.422 0.906
= 1.532 / 2 0.381
= 0.766 0.762
= 0.584

Therefore, the simplified value of the expression is 0.584.