It is not a very tough question as it has all the information's required to find the necessary answer. It is already given that 82 1/2% of a certain number is 330. It is required to find the unknown number. So we have to create an equation with a single unknown number. Let us assume the number to be = x then we can easily write the equation as given below. 82 1/2% x = 330 (165/4)%x = 330 (165/400)x = 330 x = (330 * 400)/165 = 2 * 400 = 800 So the unknown number is 800.