Help guys, I've been stuck here forever

It gets all of them right but the extra test. I don't know what is wrong. the error happens with checkio(-99.9,99.9). my output is 200 and it is supposed to be 199.8

def checkio(*args):
    if len(args) != 0:
        p = sorted(args)
        return float(format(p[-1]-p[0], '.3g'))
    else:
        return 0