Question 1093868
<pre>
                  SPEED         TIME          DISTANCE

JET               r+90         3600/(r+90)     3600

PROPELLER         r            3600/r          3600

Time Difference                 2
</pre>

{{{3600/r-3600/(r+90)=2}}}
Solve for r and evaluate r+90.

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{{{1800/r-1800/(r+90)=1}}}


common denominator is {{{r(r+90)}}}.


{{{(1800/r)r(r+90)-(1800/(r+90))r(r+90)=r(r+90)}}}


{{{1800(r+90)-1800r=r^2+90r}}}


{{{1800r+18*9*1000-1800r=r^2+90r}}}


{{{18*9*1000=r^2+90r}}}


{{{r^2+90r-18*9*1000=0}}}  or  {{{highlight_green(r^2+90r-162000=0)}}}


If choose to use general solution for quadratic equation, the discriminant is  {{{810^2}}}.


{{{highlight(r=(-90+810)/2)}}}------compute and find r+90.

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