If A driver drives a car four times a lap 10,20 30,60 kmph what is his average speed.

• avg. speed = 2xy/x+y
  so, take 10 & 20 for first two lap
  2*10*20/10+20 = 40/3......................(1)
  and,
  take 30 and 60 as same,
  2*30*60/30+60 = 40..........................(2)
  therefor,
  take avg. of two lap from 1 & 2, therefoe
  2*(40/3)*40/(40/3)+40 = 20 ans.
• 9 years agoHelpfull: Yes(21) No(7)
• Let the lap be x km
  Time taken by him to cover 4x km
  =x/10 +x/20 +x/30 +x/60 hrs
  =12x/60 hrs
  =x/5 hrs
  Therefore average speed
  =4x divided by x/5
  =4x*5/x
  =20 kmph
• 9 years agoHelpfull: Yes(17) No(1)
• Assume that length of lap is 60 km. At speed of 10 kmph, it takes 6 hours. Similarly, at speed 20, time taken 3 hours, at speed 30, time taken 2 hours and at speed 60, time taken 1 hour. Total km travelled = 240 km and Total time taken = 12 hours. Average Speed = 240/12 = 20 kmph.
• 9 years agoHelpfull: Yes(9) No(2)
• 4/(1/10+1/20+1/30+1/60)=20kmph
• 9 years agoHelpfull: Yes(7) No(0)
• 10+20+30+60/4=30kmph
• 9 years agoHelpfull: Yes(0) No(15)