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

• Jul 29th, 2005

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

#### suresh

• May 26th, 2005

41.25Kmph

#### prashanth n

• Jun 3rd, 2005

31.6 kmph (no camma given between 20 and 30 so
4 times a lap totally 12 laps ,380 km)

#### SmartMan

• Jun 5th, 2005

lap=x Km
time for 1lap=x/10 h,2 lap=x/20 h,...
all time = x/10+x/20+x/30+x/60=x/5
average speed=4x/x/5=20 kmph

#### nmodi

• Jul 17th, 2005

20 kmph is correct

• Jul 25th, 2005

30 kmph is correct bcoz 1st lap in 10 next 20
etc.. total it 120 and divide it by no. of laps
ie.120/4=30.

• Jul 29th, 2005

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

#### Raj

• Aug 23rd, 2005

(4*10*20*30*40)/(10*20*30 +10*20*60 +10*30*60 + 20*30*60) =20

#### Abhishek

• Sep 28th, 2005

(4*10+4*20+4*30+4*60)/16

=480/16

=30 kmph

#### Sheetal Salunkhe

• Nov 23rd, 2005

1st lap 10kmph,2nd 20kmph, 3rd lap 60kmph

average=(10+20+30+60)/4=120/4=30kmph

average speed=30 kmph

#### Guest

• Nov 24th, 2005

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

#### srilakshmi

• Dec 30th, 2005

Ans is 25kmph......

Here goes the explanation:

distance for the 4 speeds is same i.e.,4 times a lap

let a lap=xkm

so distance=4x for all speeds

we need to find out the avg of 4 speeeds

since avg speed=(tot dist)/(tot time)

so find out tot time

t1=4x/10

t2=4x/20

t3=4x/30

t4=4x/40

tot dist=4x+4x+4x+4x=16x;

tot time=4x(1/10+1/20+1/30+1/40);

so avg speed=tot dist/tot time;

got it!!!

i.e.,avg speed=25kmph.....

#### saurabhsingh_01 Profile Answers by saurabhsingh_01

• Jan 21st, 2006

time=x/10,x/20,x/30,x/60

total distance=4x

average speed=4x/(6x/60)=40

#### jaspreet(jagz)

• Feb 19th, 2006

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.

#### 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.

#### m_manic Profile Answers by m_manic Questions by m_manic

• Sep 2nd, 2008

Assume that total distance is 60 km.

First lap takes 6 hours and then 3 hrs, 2 hrs and 1 hr.

Total distance  = 240 km
Total Time      = 12 hrs
Average speed = 240/12 = 20 km/hr

#### microbes Profile Answers by microbes

• Oct 31st, 2008

Answer = 30 KM / Hr

Avg Distance = Total distance / Total time

= (10 + 20 + 30 + 60) / 4 = 30 Km/Hr

#### anoopmac Profile Answers by anoopmac

• May 22nd, 2009

30 is the answer becoz average  should be done by adding all and divide it by number of laps..

#### alkadamani86 Profile Answers by alkadamani86

• Sep 26th, 2010

20 kmph

#### Narendra Kulkarni

• Sep 16th, 2011

4/(1/10+1/20+1/30+1/40) = 20 km/hr.  