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Q&A #19305


Common Mistakes in Addition and Subtraction

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From: Ralph (for Teacher2Teacher Service)
Date: Feb 04, 2008 at 10:02:58
Subject: Re: Common Mistakes in Addition and Subtraction

Hi Alex,

Thank you for writing to T2T.  I'll provide you with a couple of examples
below, but first would like to suggest that anyone who is going to tackle
developing resources related to common mistakes or error patterns should
read the classic work on the subject (although it applies to grades 3-6
more than to K-2),  Robert Ashlock's Error Patterns in Computation, now in
its 9th edition. Here's one website you can look at for it:

http://www.amazon.com/Error-Patterns-Computation-Robert-Ashlock/dp/0131198866

and although the "newest edition" is a bit pricey, you can "back up one
edition or two" and get a copy for as little as 75 cents! It's really
a "must read" if you're looking at systematic computation errors.

You mentioned mixing up the addition and subtraction signs as one common
mistake, which it certainly is.  Similar "wrong operation" errors occur
particularly when an exercise is written as a "missing addend" problem,
i.e.,

3  +  ?  =  8      Students are supposed to see that the question is asking
                   what do you add to 3 to get 8, and recognize that a "5"
                   is needed to make the statement true, but the "+" sign is
                   just too "powerful a stimulus" for many, so they just
                   add 3 + 8 and write 11 as the answer.

Another common computation error occurs when students are adding,
and "regrouping" is involved--many just don't bother to regroup, so, for
example,

                28
             +  17      gets solved as
            -------
               315

Since students are always "inventing" new "systematic errors" :), it's
impossible to cover them all, but your idea of developing an application
that will "catch" many of the more common ones is excellent.  Good luck!

 -Ralph, for the T2T service

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