The ZeroSum Ruler came from a need to teach my algebra students how to balance equations such as “solve for x in: 22x + 17 = 3x + 5″, where the student has to either subtract 3x – 22x or 5 – 17 to get to the answer. My students were having a lot of difficulty with this, answering that “3x – 22x = -25x”, and so on. As it turned out, this was the BIGGEST mistake my students were making in algebra, which boils down to simple integer subtraction!
(Click the picture over there <— to go to the ruler’s video)
The ZeroSum Ruler has proven to increase understanding of integer addition and subtraction (click here to read the RESULTS of my thesis study) by 62%! One other method of teaching this idea is the “red chip/black chip” model where an amount of red (negative) chips cancel out a same amount of black chips. Sure this method works, but the chips get cumbersome. The ZeroSum Ruler works the same way as the chips except without the chips. No more buying multiple sets of checkers to perform integer addition and subtraction!
Another method that is in widespread use to teach problems such as “-22 + 17″ is the rigid number line. With this example, a student would be directed to find -25 and count 17 spaces to the right. A real-world example of “-25 + 17″ might be “Jim borrowed $25 from you and has paid you back just $17. How much does he still owe you?” In this problem, which is exactly “-25 + 17″, it is easier- and intuitive- to count up from positive 17 to 25. But how would that work on a number line? It doesn’t! But, the ZeroSum Ruler is foldable, allowing its positive numbers to align with their negative counterparts and therefore allowing students to solve integer addition and subtraction intuitively.
The ZeroSum Ruler eBook contains a ZeroSum Ruler cut-out to put together, simple instructions on how to construct and use the tool, and practice problems. You can purchase a ZeroSum Ruler eBook through CurrClick or through SmashWords.