Purple math age word problem example

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upspin
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Purple math age word problem example

Postby upspin » Tue Sep 15, 2009 2:02 am

Hello.

My question regards the first age example problem on this page (http://www.purplemath.com/modules/ageprobs.htm).
In January of the year 2000, I was thirteen times as old as my son William. In January of 2009, I was four times as old as him. How old was my son in January of 2000?


The author uses 2 variables to solve this problem however, can it be solved using one variable?

I tried and my answer did not match the answer when using 2 variables to solve the problem.

Here's what I did when using x as William's age.

Code: Select all

Age now Age in 9 years Elizabeth 13x 4(x+9) William x (x+9) Setting up my equation, I get: 13x = 4(x+9) 13x = 4x + 36 9x = 36 x = 4
So, William's age was 4 in January of 2000. But the author uses 2 variables for the problem and comes up with the age of 3.

What did I do wrong in using just one variable?

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stapel_eliz
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Postby stapel_eliz » Tue Sep 15, 2009 1:12 pm

...can it be solved using one variable?
Certainly! Instead of using variables for each of the original ages, define the other age in terms of the variable for William's age! :D
So, William's age was 4 in January of 2000. But the author uses 2 variables for the problem and comes up with the age of 3.
You did nothing wrong. The "author" was an idiot! :oops: :lol:


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