av speed = total dist/toral time =4x /x(1/10+1/20+1/30+1/60 ) =4X(60/12) =20 ans

vamsi

Jun 19th, 2006

Avg Speed==Total Distance/Total Time

One lap=x Km Time for 1 lap=x/10 h,2 lap=x/20 h,...

Total time = x/10+x/20+x/30+x/60=x/5 Hence Average speed=4x/x/5=20 kmph

Amateur

Aug 7th, 2006

Number of laps will not matter as because speed is cosistent through out the lap.

30 is the correct answer.

Jekin

Jun 30th, 2007

To sum up, the ones who believed it's 30 took an assumption that the driver drives the car in 4 different speeds for exactly the same time. But this is wrong! time = distance/speed.

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

## Editorial / Best Answer

Answered by: bhaskar s p

avg speed for 2 speeds is 2*x*y/(x+y)

therefore avg of 2*10*20/(10+20) and

2*30*60/(30+60) which is equal to 20

its correct 20

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