<PRE><B>Question 180852</B>
 a train normally travels 240km at a certain speed. one day, due to bad weather, the train&#39;s speed is reduced by 20km/h so that the journey takes two hours longer. find the normal speed.
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t = time
r = rate
t = 240/r
t+2 = 240/(r-20)
Sub for t
(240/r) + 2 = 240/(r-20)
240 + 2r = 240r/(r-20)
(240+2r)*(r-20) = 240r
(r+120)*(r-20) = 120r
{{{r^2 + 100r - 2400 = 120r}}}
{{{r^2 - 20r - 2400 = 0}}}
(r-60)*(r+40) = 0
r = 60, -40
Ignore the negative result.
r = 60 kph




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