I have been wondering about this issue for quiet some time now. I find interesting and I have not been able to come up with a solution.
This must be seen in a context of a shopping cart where you can first choose to add 1 gold bar to your cart and then add another 2, so the sum is 3.
Let's say we have these products:
1 gold bar = 40$ 2 gold bars = 80$ 3 gold bars = 110$
So when I add 1 gold bar, my cart is 40$ dollars worth. Adding another 2, then my cart is 120$ worth.
Now I have 3 gold bars in my cart.
But there is a price for 3 gold bars at 110$, and I want that price to kick in of course, because I do have 3 gold bars in my cart.
Can this be categorized as a normal knapsack issue ? Or are there any other way of looking at it ?