75. One train travels 200m from A to B with 70 km/hr and returns to A with 80 kmph, what is the average of their speed?

• distance between A and B = 200m=0.2km
  speed from A to B = 70km/hr
  time taken to go from A to B = 0.2/70 = 1/350 hr
  speed from B to A= 80km/hr
  time taken to return from B to A = 0.2/80 = 1/400 hr
  total time taken = 1/350+1/400 = 3/560 hr
  total distance covered = 0.4km
  avg speed = 0.4/3/560=74.67km/hr
  
• 11 years agoHelpfull: Yes(6) No(0)
• Average speed= 2xy/x+y
  74.67 km/hr
• 10 years agoHelpfull: Yes(0) No(0)