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

• let speed for covering distance from A to B be x
  then x=70km/hr
  also let speed for returning to same point A as y
  then y=80km/hr
  now average speed=(2*x*y)/(x+y)
  thus average speed=(2*70*80)/150
  =11200/150
  =74.67km/hr
• 11 years agoHelpfull: Yes(16) No(0)
• Ans=74.6 km/hr
  Time taken to travel from A to B=t1=0.2/70 hour
  Time taken to travel from B to A=t1=0.2/80 hour
  Total time=t1+t2=(0.2/70)+(0.2/80)=16+14/5600=3/560 Hr.
  Average speed=Total distance/Total time= 0.2+0.2/(3/560)=224/3=74.6 km/hr
• 11 years agoHelpfull: Yes(8) No(0)
• There is simple formula if train travel same distance with different speed .
  average speed is=2*x*y/x+y so by solving question by this formula ans is 74.67
• 11 years agoHelpfull: Yes(2) No(0)
• average speed=(2*x*y)/(x+y)
  then .., average speed=(2*70*80)/150
  =11200/150
  =74.67km/hr
• 11 years agoHelpfull: Yes(0) No(0)
• average speed,,, (2xy)=(x+y)
  x=70,y=80;
  Ag speed=7.467kmp
• 11 years agoHelpfull: Yes(0) No(3)