Arun, Barun and Kiranmala start from the same place and travel in the same direction at speeds of 30, 40 and 60 km per hour respectively. Barun starts two hours after Arun. If Barun and Kiranmala overtake Arun at the same instant, how many hours after Arun did Kiranmala start?

• Barun's relative speed compared to Arun is 10.Barun will need to run 6 hours to overtake Arun as Arun had already completed 60 kms in 2 hrs. By that time arun would have travelled a distance of 240km. Hence Kiranmala would have started 4 hrs after Arun.
• 12 years agoHelpfull: Yes(6) No(0)
• ANS:2hrs
  let us take time taken to cross Arun by barun is t;Arun travels same distance in t+2 time
  s is inversely proprotional to t
  so s1t1=s2t2=s3t3.where s is speed
  30*(t+2)=40t=>t=6hrs.
  s2t2=s3t3=>40t=60x(where x is time taken by kiranmala)
  x=4 kiranmala takes only 4 hr to travel the distance to cross Arun
  Barun takes 6 hrs
  so kiranamal starts after 2 hrs
  
  
• 13 years agoHelpfull: Yes(2) No(3)
• Let us assume that Arun started running at 10 AM and Barun started at 12 noon.
  So, in these two hours distance travelled by Arun is 60 km and the relative speed of Barun w.r.t Arun is 10 km/hr.
  So Barun will overtake Arun after =
  60
  10
  =6 hrs
  So, Barun reaches there at 6 PM.
  So, Kiranmala also overtakes Arun at 6 PM.
  
  Let us assume Kiranmala takes 't' time to overtake Arun and the relative speed of Kiranmala w.r.t Arun is 30 km/hr and Arun ran for 8 hrs.
  So, distance travelled by Arun is:
  While Kiranmala's distance travelled is:
  t=4 hours
  
  So, after 4 hrs, Kiranmala will start running
• 11 years agoHelpfull: Yes(2) No(0)