When you have finished this page, try the Equations 3 Quiz.
RECAP: In the previous pages, you learned about the numbers behind the mystery door and that you could have more than one of the same mystery door. On this page we will look at positive and negative numbers with magic doors. If you are not sure about the different operations with positive and negative numbers, review with the Positive and Negative Numbers section.
As you may recall from that section, adding and subtracting in reality are the combining of numbers or amounts. Here is an example with our magic doors.
3 
+ 

= 
2 
In this case in order to take negative three away from both sides, it must be a positive three as a negative three and a positive three equals zero or nothing. Remember, what you do to one side of the equation must be done to the other side. Therefore, three must be added to the two on the right side of the equation.
3

+ 

= 
2


= 
5 