He has 80% of his sheep left. If he sold 40 out of 200 sheep, the fraction would be 40/200. But we are dealing with percentage, so we need the denominator to be 100. And to do that, we need to divide the fraction by 2. Once we do that we get 20/100. So now we subtract 20 from 100 to get 80, and that means 80% is the answer. I hope this helped you, sweetie.