# Common Notion 3

- Author:
- Mathew Purser

**If equals are subtracted from equals, then the remainders are equal.**Consider our completed puzzles from CN2, if you remove the same pieces from each puzzle, the remaining puzzles are still equal.

## Tool Practice

Use the applet below to convince yourself of CN3
HINT: Use the slide bar to adjust the size of the red rectangle, notice since the large squares are equal and the red rectangles are equal, that the remaining blue areas are also equal.