A vending machine in an office building sells bottled beverages. The machine keeps track of all changes in the number of bottles from sales and from machine refills and maintenance. This record shows the changes for every 5-minute period over one hour.
What might a positive number mean in this context? What about a negative number?
What would a “0” in the second column mean in this context?
Which numbers—positive or negative—result in fewer bottles in the machine?