The ZeroSum Ruler: a math tool for adding and subtracting

Posted by Shana Donohue in Boston, MA on 12/22/10

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If you liked what you read in the ZeroSum Ruler's free
eBook, this eBook contains a ZeroSum Ruler cut-out, simple
instructions on how to construct and use the tool, and
simple integer addition and subtraction problems to try,
which are at the root of may higher-level mathematics
problems (see below).

To get an idea of what you may find in this book, let's
walk through a typical problem that stumped my students
before being introduced to the ZeroSum Ruler:

To solve 8x + 11 = 15x + 27, would you:

1) subtract 8x?

2) subtract 11?

3) subtract 15x?

4) subtract 27?

My students would subtract 11 from both sides to get:

8x = 15x + 16

And then go on to tell me that:

-23x = 16

Wait, where the heck did they get that -23x?? 8x - 15x
= -7x, not -23x!

They were confusing the rules of addition and subtraction
with the rules for multiplication and had no idea how to go
about solving 8 - 15! I soon realized that my students
needed a better way to learn simple integer addition and
subtraction. This is how the ZeroSum Ruler came to be.

The ZeroSum Ruler has proven to increase understanding of
integer addition and subtraction by 62%! If you visit my
blog at http://zerosumruler.wordpress.com/, you can see the
results of my thesis as well as videos on how the tool
works.

HaPpY Calculating!

Sincerely,
Shana Donohue

The ZeroSum Ruler: a math tool for adding and subtracting