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# M07-11

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Math Expert
Joined: 02 Sep 2009
Posts: 50002

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16 Sep 2014, 00:34
00:00

Difficulty:

55% (hard)

Question Stats:

75% (01:20) correct 25% (02:42) wrong based on 114 sessions

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A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?

A. 24
B. 40
C. 48
D. 96
E. 120

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Math Expert
Joined: 02 Sep 2009
Posts: 50002

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16 Sep 2014, 00:34
1
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Official Solution:

A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?

A. 24
B. 40
C. 48
D. 96
E. 120

Time to travel 4 kilometers at 120 kilometers per hour is $$\text{time}=\frac{\text{distance}}{\text{rate}}=\frac{4}{120} \text{hours} = \frac{4*3,600}{120} \text{seconds} = 120 \text{seconds}$$;

Time to travel 2 kilometers at a regular speed is $$120+30 = 150 \text{seconds} = \frac{150}{3,600} = \frac{1}{24} \text{hours}$$;

So, the speed of a train is $$\text{rate}=\frac{\text{distance}}{\text{time}}=\frac{2}{(1/24)}=48$$ kilometers per hour.

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Joined: 17 Sep 2015
Posts: 12
GMAT 1: 760 Q50 V42
GPA: 3.65

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29 Oct 2015, 17:13
seems like a 700 level problem, not sub-600.
VP
Joined: 07 Dec 2014
Posts: 1104

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08 Jan 2016, 18:14
2
let s=speed
2/s-4/120=1/120
s=48 kph
Intern
Joined: 06 May 2016
Posts: 14

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04 Aug 2016, 11:48
time taken for second train travelling at 120Kmph= 4/120 = 1/30 hr

Total time for the first train travelling at x speed = 30/3600 + 1/30 = 1/24 hr

speed = distance /time= 2km/(1/24) hr = 48 kmph
Intern
Joined: 27 Apr 2011
Posts: 47
GMAT Date: 06-13-2017

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01 Aug 2018, 02:46
The question is absolutely 700 level. Great Language trap.
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Hope it's clear.
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Please +1 KUDO if my post helps. Thank you.

Re: M07-11 &nbs [#permalink] 01 Aug 2018, 02:46
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# M07-11

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