This illustration is actually four in one: Chips, Net Worth, Operations, and Generic. In each one of those, you have a number line, and the operations you do will be illustrated on it with arrows.
In Chips, you add either positive or negative chips to a bag. As you do so, the program draws an arrow on the number line to illustrate the addition of that amount. For example, if your bag already has −6 chips, and you add 3 positive chips, it draws an arrow from −6 to −3 on the number line. Net Worth is very similar, but instead of chips, you drag either debts or assets to the bags.
In the "Operations" activity, you start with zero, and you decide how much to add or subtract to that, and then you can do it again: decide another amount to add or subtract. These amounts to add or subtract are titled "assets" and the program shows you your final net worth. The operations are shown with arrows on the number line as you click.
Lastly, in the "Generic" activity, you do the same as in "Operations", but the language does not refer assets. The starting point is 1. You choose to add or subtract two different numbers, and the program shows those with arrows on the number line plus a mathematical expression (addition/subtraction), which you can choose to simplify.
In "Generic", you can choose between a number line from −10 to 10, from −30 to 30, or from −100 to 100. You can even display two number lines and show different additions and subtractions on each.
Credit: This activity is created by PhET
Screenshot from the activity:
