<span>You know that 20%, or 1/5 equals 64 so you multiple 64 by 5 to get the full 100% number. In this question 320. You then divide 320 by 100 to get the value per 1%. Then multiple this by 50 to get 160. </span>
<span>To check that you have the right answer, you divide 320 by 100 then multiple by 20 and if you get 64, you have the right answer. </span>