WME@Kimpton Middle
Understanding Negative Integers III
You are saving money to buy a cool MP3 player. And you
can use integers to keep track of your progress. Say we use
blue chips and red chips this way:
 A blue chip represents 1 (dollar), two blue chips 2, and so on.
 A red chip represents −1 (dollar spent), two red chips −2, and so on.
 Putting chips of either color in the piggy bank models additon.
 Removing chips of either color from the piggy bank models subtraction.
Let's see how this model works.
8 + (−3) means: The piggy bank starts with 8 blue chips, now add 3 red chips.
5 − (−3) means: The piggy bank starts with 5 blue chips, now remove 3 red chips.
This tool helps you visualize how to keep count.
Do 8 + (−3) this way:
 First add 8 blue chips in the above grid (the piggy bank).
 Now add red chips. How many red chips
do you need to put in?
 What is the answer? (Hint: how many unpaired blue chips remain?).
Next, do 5 − (−2) this way:
 Observe we have 5 blue chips and 3 redblue pairs in the grid already.
 Now remove red chips.
How many red chips do you need to remove?
 What is the answer for 5 − (−2)?
