Question 831317
Exactly the same exercise, :


http://www.algebra.com/algebra/homework/Average/Average.faq.question.831176.html

and 

Same general problem but just different example:  Look-up problem number 830872
http://www.algebra.com/algebra/homework/word/travel/Travel_Word_Problems.faq.question.830872.html 



--------------------REQUEST FOR SOLUTION WAS STRONGLY DESIRED----------HERE!-----


The data table went like this:
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_____________speed____________time____________distance
Jet__________r+80_____________h-2_______________3960
Propeller____r_________________h________________3960


R*t=d the uniform rates equation for travel, R meaning rate, t for time, d for distance.

JET: (r+80)(h-2)=3960;
PROP: rh=3960. 
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Use the simpler equation in two ways.  For substitution directly for {{{r*h}}} and in the form of 

{{{h=3960/r}}}.


Using {{{R*T=D}}}, the jet equation is {{{(r+80)(h-2)=3960}}}
{{{rh+80h-2r-160=3960}}}
Substituting for {{{rh=3960}}}, obtain {{{3690+80h-2r-160=3960}}}
{{{80h-2r-160=0}}}
{{{40h-r-80=0}}}
Substitute for h FROM the simpler equation
{{{40(3960/r)-r-80=0}}}
{{{40(3960)-r^2-80r=0}}}
{{{highlight_green(r^2+80r-158400=0)}}}


Using the general solution for a quadratic equation but omitting the expression and steps:
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Propeller Plane
r=360 mph
h=11 hours
Jet Plane
r+80=440 mph
h-2=9 hours
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