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# A car travels the first one-third of a certain distance with a speed

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Math Expert
Joined: 02 Sep 2009
Posts: 61385
A car travels the first one-third of a certain distance with a speed  [#permalink]

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06 Jan 2020, 06:34
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Question Stats:

75% (02:17) correct 25% (00:36) wrong based on 4 sessions

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A car travels the first one-third of a certain distance with a speed of 10 kmph, the next onethird of the distance with a speed of 20 kmph and the last one-third distance at 60 kmph. Find the average speed of the car for the whole journey.

A. 18 kmph
B. 20 kmph
C. 25 kmph
D. 30 kmph
E. 40 kmph

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CrackVerbal Quant Expert
Joined: 12 Apr 2019
Posts: 385
Re: A car travels the first one-third of a certain distance with a speed  [#permalink]

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10 Jan 2020, 01:40
Since 1/3rd of the distance is to be taken, let us take the total distance to be 3d kms. There are 3 segments each of d kms then.

For the first segment, time taken = $$\frac{d}{10}$$ hours

For the second segment, time taken = $$\frac{d}{20}$$ hours

For the third segment, time taken = $$\frac{d}{60}$$ hours

Total time taken = $$\frac{d}{10}$$ + $$\frac{d}{20}$$ + $$\frac{d}{60}$$ = $$\frac{d}{6}$$ hours.

Now, we know that Average Speed = $$\frac{Total Distance Travelled }{ Total time taken}$$.

Substituting the relevant values, we have,
Average speed = $$\frac{3d }{ (d/6)}$$ = 18kmph.

The correct answer option is A.

Hope that helps!
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Re: A car travels the first one-third of a certain distance with a speed   [#permalink] 10 Jan 2020, 01:40
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