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M09-09

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Math Expert
Joined: 02 Sep 2009
Posts: 42571

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15 Sep 2014, 23:39
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Question Stats:

78% (01:35) correct 22% (02:11) wrong based on 112 sessions

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The train consists of 6 carriages, 20 meters long each. The gap between the carriages is 1 meter. If the train is moving at a constant speed of 60 km/h, how much time will it take the train to run through a 1 kilometer tunnel?

A. $$1\frac{1}{8}$$ minutes
B. $$1\frac{1}{2}$$ minutes
C. $$1\frac{3}{4}$$ minutes
D. 2 minutes
E. $$2\frac{1}{4}$$ minutes
[Reveal] Spoiler: OA

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15 Sep 2014, 23:39
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Official Solution:

The train consists of 6 carriages, 20 meters long each. The gap between the carriages is 1 meter. If the train is moving at a constant speed of 60 km/h, how much time will it take the train to run through a 1 kilometer tunnel?

A. $$1\frac{1}{8}$$ minutes
B. $$1\frac{1}{2}$$ minutes
C. $$1\frac{3}{4}$$ minutes
D. 2 minutes
E. $$2\frac{1}{4}$$ minutes

The length of the train is $$6*20$$ plus five 1 meter gaps, so it's $$6*20+5=125$$ meters;

The length that should be traveled by train is $$1+0.125=1.125$$ kilometers;

$$\text{Time}=\frac{\text{Distance}}{\text{Rate}}=\frac{1.125}{60}$$ hours or $$\frac{1.125}{60}*60=1.125=1\frac{1}{8}$$ minutes.

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14 Mar 2015, 04:56
Bunuel wrote:
Official Solution:

The train consists of 6 carriages, 20 meters long each. The gap between the carriages is 1 meter. If the train is moving at a constant speed of 60 km/h, how much time will it take the train to run through a 1 kilometer tunnel?

A. $$1\frac{1}{8}$$ minutes
B. $$1\frac{1}{2}$$ minutes
C. $$1\frac{3}{4}$$ minutes
D. 2 minutes
E. $$2\frac{1}{4}$$ minutes

The length of the train is $$6*20$$ plus five 1 meter gaps, so it's $$6*20+5=125$$ meters;

The length that should be traveled by train is $$1+0.125=1.125$$ kilometers;

$$\text{Time}=\frac{\text{Distance}}{\text{Rate}}=\frac{1.125}{60}$$ hours or $$\frac{1.125}{60}*60=1.125=1\frac{1}{8}$$ minutes.

Hi Bunuel,

Your question is a little bit ambiguous.
When one say that the train is entering into tunnel, the total time train was inside the tunnel is the time taken by the train when 1st coach enters the tunnel till the last coach exits the tunnel.

That makes 1 km + 125 + 125.

I don't know why did you pick 1 km + 125 m ?

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21 Nov 2015, 06:01
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How do you arrive at this step:

"The length that should be traveled by train is 1+0.125=1.125 kilometers;"

I understand the steps before and after that, just not this part - thanks!

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22 Nov 2015, 04:21
LostinNY wrote:
How do you arrive at this step:

"The length that should be traveled by train is 1+0.125=1.125 kilometers;"

I understand the steps before and after that, just not this part - thanks!

0.125km ---------------------------------------------- 1km
------|------------------------------------------------|

In red is a train and in blue a tunnel. The whole train to run through the tunnel, it should travel the length of a train plus the length of the tunnel.
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18 Feb 2016, 07:28
Hi Bunuel,

I'm struggling to understand why/how you're multiplying by 60 to cancel out the rate.

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18 Feb 2016, 07:30
safaria25 wrote:
Hi Bunuel,

I'm struggling to understand why/how you're multiplying by 60 to cancel out the rate.

By multiplying by 60 I'm just converting hours into minutes.
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09 Mar 2016, 00:11
Hi Bunnel,

Can you illustrate it more please ?

Thanks
Eman

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09 Mar 2016, 10:38
Emaco wrote:
Hi Bunnel,

Can you illustrate it more please ?

Thanks
Eman

Please go through the discussion above and ask more specific question if doubts remain.
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14 Jul 2017, 06:28
I think this is a high-quality question and I don't agree with the explanation. the answer is incorrect. total distance traveled by train to cross the tunnel will be 1.25 KM not 1.125. we cannot chopp of the crarriages length at exit of the tunnel

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14 Jul 2017, 06:39
Sushilait84 wrote:
I think this is a high-quality question and I don't agree with the explanation. the answer is incorrect. total distance traveled by train to cross the tunnel will be 1.25 KM not 1.125. we cannot chopp of the crarriages length at exit of the tunnel

How did you get 1.25 km? We ARE counting the length of the tunnel + the length of the train.

The length of the train is $$6*20$$ plus five 1 meter gaps, so it's $$6*20+5=125$$ meters;

The length that should be traveled by train is $$1+0.125=1.125$$ kilometers (1 kilometer and 125 meters);
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09 Oct 2017, 05:44
This is a poor quality question. The total length travelled should be 1000+125+125

Posted from my mobile device

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09 Oct 2017, 06:00
kishor1 wrote:
This is a poor quality question. The total length travelled should be 1000+125+125

Posted from my mobile device

Hope the following helps yo understand better: https://gmatclub.com/forum/m09-183817.html#p1888020
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08 Nov 2017, 11:20
That is from when the front enters the tunnel to when the front exits the tunnel. But the body of the train is still 125meters inside the tunnel.

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Re: M09-09   [#permalink] 08 Nov 2017, 11:20
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