The hungry box of candy

Ask your 7th grader to tell you a story in which the value of a variable is negative. The story we were telling today is of the box of candy that, instead of adding to our pile of chocolates, takes chocolates from the common stash. So, for example, if x = -5, someone brings a box of chocolates x, but instead of adding to the pile of chocolates, the box grabs five chocolates from the pile.