A fly is flying between two trains, each travelling towards each other on the same track at 60 km/h. The fly reaches one engine, reverses itself immediately, and flies back to the other engine, repeating the process each time. The fly is flying at 90 km/h. If the fly flies 180 km before the trains meet, how far apart were the trains initially?

• Ans: 240km
  
  
  let the reqiured distance be D.
  relative speed of the trains = (60+60)
  time taken by the two trains to meet = (total distance between them)/their relative speed =D/(60+60)...........(1)
  
  speed of fly=90km/hr and distace travelled by it = 180.
  so time for which it flies = 180/90= 2 ............(2)
  
  from equation 1 & 2 we have...D/(60+60) = 2
  =>D= 240
• 11 years agoHelpfull: Yes(35) No(4)
• its 240kms.
  
  when fly flies first 90km, total distance traveled by both train is (60+60)=120km.
  for next 90km by fly, trains again travel 120km, hence total distance between two trains initially is 120km + 120km = 240kms.
• 11 years agoHelpfull: Yes(7) No(1)
• 240 kms as fly flies for 2hrs and relative speed is 120km/hr, so 120*2=240
• 11 years agoHelpfull: Yes(2) No(1)
• time taken by the fly to cover 180km at speed 90km/h= D/T = 180/90 = 2hr
  now as the train are travelling in opp direction so
  relative speed = S1 + S2
  = 60 + 60 = 120km/hr
  Time = 2 hr ( equals the time taken by the fly cuz it will travel only till the
  trains dun meet)
  
  Distance = T * S
  = 120 * 2
  = 240km ANS.
• 11 years agoHelpfull: Yes(2) No(0)
• Relative speed of fly with any train= (90+60) = 150km/hr
  Distance travelled= 180km
  Time taken= 6/5hr..........eqtn 1
  
  Now the relative speed of the trains are (60+60)= 120km/hr
  So the distance will be= speed*time= 120*6/5= 144km..
  
  
• 11 years agoHelpfull: Yes(1) No(0)
• what are the options
• 11 years agoHelpfull: Yes(0) No(1)
• the fly took 2hrs to travel till they meet
  hence the trains travelled for two hours with relative speed of 60+60=120kmph
  distance they covered=initial distance=2*120=240km
• 11 years agoHelpfull: Yes(0) No(0)