3.2: Hot Air Balloon
This activity is intended to supplement Algebra I, Chapter 2, Lesson 3.
Problem 1 – Integer Addition
Press PRGM and find the HOTAIR program in the list.
Press ENTER to load the program.
Use the model to find the sum
Press ENTER to choose option 1, Integer Addition.
Note: The right arrow adds a helium bag to the balloon, and the left arrow adds a sand bag.
Press ENTER to start and press
The sum

2 signifies adding two helium bags, which raises the balloon2 units . Press the right arrow twice. 
−6 signifies adding six sand bags, which lowers the balloon6 units . Press the left arrow six times.
The balloon’s resulting position is the sum.
With your partner, translate the following expressions into “balloon language” and use the model to find the sum. Remember to reset the balloon to ground level each time. When you are finished, press ENTER to return to the menu.

−4+7=−−−− 
7+3=−−−− 
5+(−7)=−−−− 
−5+(−3)=−−−−
Problem 2 – Missing Addend
Find the value of
Arrow down to option
You are given the value of
Input the value for
Press ENTER to start and press
In terms of the balloon, there are four sand bags. Press the left arrow four times.
You can see the balloon at the bottom of the screen. Now there is also a target balloon to the right. The task is now to find the value of
The target balloon, on the right, is positioned at the value of the sum.
The target balloon is above your balloon’s position, so you need to add helium bags. Press the right arrow to add helium bags until the balloons line up. Count as you press to find how many helium bags you added. For this example,
With your partner, translate the following equations into “balloon language” and use the model to find the missing addend. When you are finished, press ENTER to return to the menu.
1.
2.
3.
4.
Problem 3 – Integer Subtraction
The model also provides a way of visualizing the subtraction of integers. As with addition, positive integers are represented by helium bags and negative integers by sand bags. However, subtraction is the operation of taking off a bag. For example, the expression
Arrow down to option 3, Integer Subtraction, and press ENTER.
Note: The right arrow removes a helium bag, and the left arrow removes a sand bag.
Reset the balloon at ground level by pressing the right arrow.
Move the balloon to its starting point,
To remove
With your partner, translate the following expressions into “balloon language” and use the model to find the difference. When you are finished, press ENTER to return to the menu.

2−7=−−−− 
−3−1=−−−− 
5−(−2)=−−−− 
−4−(−7)=−−−−
Problem 4 – Missing Subtrahend
This model shows two balloons side by side—like the model from Problem 2, except that it is used to find a missing subtrahend rather than a missing addend.
Arrow down to option 4, Missing Subtrahend, and press ENTER.
For example, find the value of
Input the value for
Your balloon is at the top of the screen, and the target balloon to the right represents the difference.
Reset the balloon at ground level by pressing the right arrow.
Note: The right arrow removes a helium bag, and the left arrow removes a sand bag.
Move the balloon to its starting position,
The target balloon is above your balloon’s position, so you need to remove sand bags. Press the left arrow to remove sand bags until the balloons line up. Count as you press to find how many sand bags you removed. For this example, you should find that
With your partner, translate the following equations into “balloon language” and use the model to find the missing subtrahend. When you are finished, press ENTER to return to the menu.
1.
2.
3.
4.
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