Two horses begin running on an oval course at the same time.

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Two horses begin running on an oval course at the same time. [#permalink]

29 Apr 2012, 22:23

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Question Stats:

57% (02:02) correct

42% (01:28) wrong

based on 42 sessions

Two horses begin running on an oval course at the same time. One runs each lap in 9 minutes; the other takes 12 minutes to run each lap. How Many minutes after the start will the faster horse have a one lap lead?

A. 36
B. 12
C. 9
D. 4
E. 3

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Re: Word Problem [#permalink]

29 Apr 2012, 23:12

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The best approach in my view is like this:
Check from the answer options.
As one horse completes the lap in 9 minutes and the other in 12 minutes, the answer is definitely greater than 12, because by 12 minutes, faster on completes 12/9 = 1.33 laps and the slower one completes only 1 lap, which results in a gap of 1.33 - 1 = 0.33 laps, which is less than 1 lap.
The only option looks feasible is option-A, ie., 36 min.
With out checking we can go for that. But let us check:
After 36 min, faster one completes 36/9 = 4 laps and
slower one completes 36/12 = 3 laps.
The faster one covered exactly one more lap than the slower one did.
Answer 'A'
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Ravi Sankar Vemuri

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Re: Word Problem [#permalink]

29 Apr 2012, 23:31

Thank you for the clarification Ravi. Your method makes sense to me.

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Re: Two horses begin running on an oval course at the same time. [#permalink]

29 Apr 2012, 23:51

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rakp wrote:

The rate of the faster horse is 1/9 lap/minute;
The rate of the slower horse is 1/12 lap/minute;

Their relative rate is 1/9-1/12=1/36 lap/minute;

The faster horse to gain one full lap will need time=distance/rate=1/(1/36)=36 minutes.

Answer: A.

Hope it's clear.
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Re: Two horses begin running on an oval course at the same time. [#permalink] 29 Apr 2012, 23:51

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Two horses begin running on an oval course at the same time.

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Two horses begin running on an oval course at the same time.

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