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Assigning Variables for Age

Date: 02/21/2003 at 23:46:45
From: G. G.
Subject: How to calculate age of individuals current and present

John is 32. He is twice as old as Jim was when John was as old as Jim 
is now. How old is Jim?

I don't understand how to assign the variables that will give me the 
answer to this problem.


Date: 02/22/2003 at 20:55:30
From: Doctor Peterson
Subject: Re: How to calculate age of individuals current and present

Hi, G. G.

My technique is to define a variable each time a new "when" is 
mentioned. We'll start with

    x = Jim's age now

So we have

    He is twice as old as Jim was when 

    32  =   2    *        (x - a)

where this "when" is "a" years ago. Continuing,

    John was as old as Jim is now.

        (32 - a)    =      x

In other words, I pull the subordinate clause out into its own 
sentence like this:

    He is twice as old as Jim was a years ago.

    a years ago, John was as old as Jim is now.

See if you can take this and solve for x. If you need more help, 
please write back and show me how far you got.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/ 
Associated Topics:
Middle School Algebra
Middle School Word Problems

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