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Choosing an Unknown


Date: 08/06/97 at 20:06:50
From: Rachel
Subject: I have a word problem question.

What is the easiest way to do a hard word problem?


Date: 08/12/97 at 17:28:50
From: Doctor Mike
Subject: Re: I have a word problem question.

Dear Rachel,
   
For most people, choosing the unknown is the hardest part. Like
 
   "Let X be the unknown number of gallons"
   "Let D be the distance traveled"
   "Let A be the angle the see-saw makes with the ground"

depending on what the problem is about. You really need
to think carefully about this step. It's important to get
a good start.
    
Then you usually take information given to you and put it
into an equation form like

   X*pi = 35
   D+55 = 100
    3*A = 90
   
You may be given the facts to make 2 equations. From this
point on, you work with the numbers and the equations, and
try to find the answer. This step is the "pure algebra"
step. The most important tool you have to work with is the
principle that you can do EXACTLY THE SAME THING to both
sides of an equation, and you will wind up with another true
thing. Here are some examples:
   
   Start out with D+55 = 100.  Subtract 55 from both sides
   and you get D+55-55 = 100-55, which simplifies to D = 45.
   
   Start out with 3*A = 90.  Divide both sides by 3 and you
   get (3*A)/3 = 90/3, which simplifies to A = 30.  
   
This is about all I can say in general about word problems,
but if you send one in to Dr. Math we can show you how to
work it out.  I find I learn pretty well by looking at some
examples, and maybe you will too. 

-Doctor Mike,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
    
Associated Topics:
Middle School Word Problems

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