Pre-Algebra Review Topic
 Add & Subtract Signed Numbers with Algebra Tiles
 Topic Index | Algebra Index | Regents Exam Prep Center

 

See Homemade Algebra Tiles
for template for making tiles for your students to use in class.

 

 Key: TRtile6.gif

 *Be sure to stress that a red tile and a yellow tile (of the same size) will cancel each other out (will add to 0) and will be removed from the table.

 
1.  Addition:   Show  3  +  ( -5 )  =  -2
 

TRtile9.gif

 

2.  Subtraction:  Show  5  -  ( -2 )  =  7

The concept of "subtraction" is the removal of a certain number of tiles.   In this problem it is necessary to remove 2 negative (red) tiles.  Since positive five contains NO negative tiles to be removed, it is necessary to introduce the negative (red) tiles.  Notice the middle step of adding 0 (one red and one yellow) to the problem twice.

TRtile10.gif

Or explain as:

A simpler way to explain this process, and to reinforce the "rules" for subtracting signed numbers, is to start with five positive tiles (yellow) and two negative tiles (red) and then instruct the students to "change the sign" of the tiles being subtracted by replacing them with positive yellow tiles.

TRtile11.gif