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Q&A #19967


Writing algebraic expressions from verbal phrases

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From: Gail (for Teacher2Teacher Service)
Date: Dec 07, 2008 at 17:38:46
Subject: Re: Writing algebraic expressions from verbal phrases

Hi Jennifer,

This is always difficult for my middle school students, as well. I start out
by giving them a situation like this one: Andy's brother is three years
younger than Andy is. I put the "three years younger than Andy" in a
different color on the overhead or power point, so that it stands out from
the rest of the problem. Then I ask them what they need to know to figure
out how old Andy's brother is. They tell me right away that they need to
know Andy's age.  The next slide conveniently has that info:

"Andy's brother is three years younger than Andy is. Andy is 12 years old."

I ask them how they will figure out how old the brother is, and they all
know you have to subtract 3 from Andy's age. We talk about how to write
that in "math" or "algebra", and determine it is 12 - 3. I ask them why we
can't write it 3 - 12, and it is pretty clear that the age couldn't be -9,
or probably wouldn't be, at least (there is always someone who wants to
argue that it could be).

Then we all look back at the original statement, and figure out why the
word "from" is so important.

We make up some more situations, write them with algebra, make sure they
make sense, and there doesn’t seem to be as much trouble with the idea
anymore. I hope this helps you get started, at least.

 -Gail, for the T2T service

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