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 
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 R9
Missouri
 
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