Your $15 will initially by you 15 sweets. From that you will get 15 wrappers though. Thus you can trade it for another 5 sweets, bringing a total to 20 initially. Your five sweets will equate to 5 more wrappers, which will get you one more sweet and two left over wrappers (you have 21 sweets total now). The one sweet will yield one additional wrapper, which combined with the other two will be one final sweet. You'd end up with 22 sweets and 1 leftover wrapper...correct?
haha, I'm right, right?
Thats what I thought!