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:

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- Aug 18th 2006, 01:01 AManjanaquadratic 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: - Aug 18th 2006, 01:12 AMCaptainBlackQuote:

Originally Posted by**anjana**

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

similarly at the higher speed it would take:

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

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

$\displaystyle

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

$

which we can rearrange to:

$\displaystyle

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

$

Which has two solutions and you need the poitive one.

RonL