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Writing Expressions with Variables


Date: 09/13/98 at 21:56:54
From: Uriah Rice
Subject: How to do the problem and the answer to the problem

Write an expression that represents a $500 donation plus $5 for every  
event. Let n represent the number of events. 

I do not understand what the problem wants me to write.


Date: 09/14/98 at 08:15:08
From: Doctor Rick
Subject: Re: How to do the problem and the answer to the problem

Hi, Uriah. 

I presume you are being guided through the solution of a word problem.
Either you were given the word problem, and you are going through it 
one step at a time, or you are just practicing what you would do if 
you had the whole problem. 

An expression is a collection of numbers and variables connected by
arithmetic operations (add, multiply, etc.) so that if you worked out 
all the arithmetic, you would get a number. In this case, the number 
you would get would be the total payment.

Let's say you knew there were 4 events. Could you then work out how 
much to pay? It would be:

   500 + 5 * 4

in dollars. This is an expression. You can work it out and get the 
answer of 520. (In case this is your first time working with math on a 
computer, we use "*" to represent multiplication, because "x" might be 
a variable.)

In fact, you don't know how many events there are. But whatever that 
number turned out to be, you could put it in place of the "4" in the 
expression and work it out in just the same way. So what we do is use 
a letter as a name to stand for whatever number we will end up putting 
there. This is a variable. It is sort of a place holder for a number.

You were asked to use the letter "n" to represent the number of 
events. That means "n" will be our variable, and we can put it in 
place of the 4, like this:

   500 + 5 * n

When multiplying by a variable, we don't need to write the "*". You 
can just write:

   500 + 5n

I hope this helps you work out other problems in writing expressions.

- Doctor Rick, The Math Forum
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Associated Topics:
Middle School Word Problems

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