a train travels a distance of 300km at a constant speed.if the speed of the train is increased by 5km/hr,the journey would have taken two hours less.find the initial speed of the train?

• we know that, s = d / t
  distance = 300 km
  initail speed ( s) , new speed = s + 5
  initial time taken ( t ) = 300 / s and new time taken = 300 / s + 5
  so now, according to the ques :
  300 / s + 5 + 2 = 300 / s
  2 = 300 / s + 300 / s + 5
  2 = (300s + 1500 - 300s) / s 2 + 5s
  2s 2 + 10s - 1500 = 0
  s 2 + 5s + 750 = 0
  s2 - 25s + 30s - 750 = 0
  s ( s - 25) + 30 ( s - 25 ) = 0
  s = 25 or -30
  
  answer: 25 km / hr..
• 11 years agoHelpfull: Yes(3) No(3)
• Let the speed of the train be "x km/hr"
  so time=distance/speed
  =>time=300/x
  now if we will increse the speed of train,then it will take 2hr less.
  new speed =x+5
  SO comparing time we can form equation as
  (300/x)-(300/x+5)=2
  Solving the equation x=25 (As we will take the positive calue of x)
• 11 years agoHelpfull: Yes(3) No(0)
• let the speed=x km/hr
  time to travel 300km=300/x hr
  at a speed of x+5km/hr=300/(x+5) hr
  300/x - 300/(x+5) = 2
  (x+30)*(x-25)=0
  x=25 is the answer(x=-30 not possible since x should be positive )
• 11 years agoHelpfull: Yes(2) No(0)
• let x1 be the initial speed of train,
  x1=300/t1
  and x2 be the increased speed , x2 = (x+5)=(300/t1 + 5)
  x1*t1=x2*t2(if distance is same then s1*t1=s2*t2)
  (300/t1)*t1=(300/t+5)(t1-2)
  this gives t1 = 10hrs
  x1=300/10
  x1=30km/hr.
  
• 11 years agoHelpfull: Yes(0) No(1)
• 25 km/hr
  
  
  
  
  
  
  
  
  
  
  
  
  
• 10 years agoHelpfull: Yes(0) No(1)