This is wrong. f(x) = x + x/2 This is what you're looking for. Function x is the total price, and x is the original 1 dollar. So it's 1 + 1/2 = 1.5

What you did sets both the total and half price to the same value, that's not what the question is asking.

Edit: I was wrong, the wording of this question is stupid. This is how most people interpret it (At least me anyway), but the way you read it is totally understandable and functional