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Discussion: All Lesson Plans in Calculus on TI Calculator
Topic: teacher needs help!


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Subject:   teacher needs help!
Author: magnus
Date: Dec 14 2004
Hi, I teach calculus at a rural school, and am having problems with a particular
word problem.  

It reads as follows:  A car traveling north at 60 mph and a truck traveling east
at 45 mph leave an intersection at the same time. At what rate is the distance
between them changing 2 hours later?

The answer in the answer key is 75 mph which would be the pythogorean triple of
45 and 60.  However, when I work the problem out with what I know about related
rates (and it seems that you all know a lot more than me) I get approximately
74.2 mph.  

Who is right?  Is the real answer 75, and it is just a coicidence that 75 is the
pythogorean triple?  What answer do you get, and how did you get it?  To solve
this problem, I'm using the concept of "related rates, dx/dt, & dy/dt," which
would make sense, since that is the title of the section this problem comes
from.

Thanks for helping.
John Jones
Trenton R-9
Missouri

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