# quadratic equations

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• August 18th 2006, 01:01 AM
anjana
quadratic equations
a train covers a distance of 300km at a constant speed .if the speed of the train is increased by 5km/hr the journey would have taken 2 hour less.find the original speed of train?

:confused:
• August 18th 2006, 01:12 AM
CaptainBlack
Quote:

Originally Posted by anjana
a train covers a distance of 300km at a constant speed .if the speed of the train is increased by 5km/hr the journey would have taken 2 hour less.find the original speed of train?

:confused:

If the original speed is $v \mbox{ km/hr}$, then the time to travel $300 \mbox{ km}$ is:

$t_1=\frac{300}{v}\ \mbox{hr}$,

similarly at the higher speed it would take:

$t_2=\frac{300}{v+5}\ \mbox{hr}$.

But we are told $t_1=t_2+2 \mbox{ hr}$, so:

$
\frac{300}{v}=\frac{300}{v+5}+2
$

which we can rearrange to:

$
-2 v^2 + 10 v - 1500=0
$

Which has two solutions and you need the poitive one.

RonL