The range of possible values are 480-520.
Since we are either adding or subtracting 4%, first we need to find 4% of 500. In order to do that, we multiply the whole by the percentage.
500*4% = 20.
Now, to find the high end, we add that to 500 and to get the low end, we subtract it from 500.
500 + 20 = 520
500 - 20 = 480