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Barry walks from one end to the other of a 30-meter long

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Barry walks from one end to the other of a 30-meter long [#permalink] New post 20 Oct 2012, 10:12
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Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway. When he reaches the end, he reverses direction and continues walking with the same speed, but this time it takes him 120 seconds because he is traveling against the direction of the moving walkway. If the walkway were to stop moving, how many seconds would it take Barry to walk from one end of the walkway to the other?

A) 48
B) 60
C) 72
D) 75
E) 80
[Reveal] Spoiler: OA
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Re: Barry walks from one end to the other of a 30-meter long [#permalink] New post 20 Oct 2012, 12:55
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nitzz wrote:
Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway. When he reaches the end, he reverses direction and continues walking with the same speed, but this time it takes him 120 seconds because he is traveling against the direction of the moving walkway. If the walkway were to stop moving, how many seconds would it take Barry to walk from one end of the walkway to the other?

A) 48
B) 60
C) 72
D) 75
E) 80


Let Barry's speed be x m/s and walkway's speed by y m/s. We need to find 30/x.

If Barry walks in the direction of the moving walkway, the total speed is x + y. Time taken is 30/(x+y)
Thus, 30/(x+y) = 30

=> x + y = 1 ... (1)

If Barry walks against the moving walkway's direction, total speed is x-y. Time take is 30(x-y)
Thus, 30/(x-y) = 120

=> x - y = 1/4 ... (2)

Add (1) and (2),
=> 2x = 5/4
=> x = 5/8

therefore, 30/x = 48

Right answer is A.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink] New post 22 Oct 2012, 07:10
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nitzz wrote:
Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway. When he reaches the end, he reverses direction and continues walking with the same speed, but this time it takes him 120 seconds because he is traveling against the direction of the moving walkway. If the walkway were to stop moving, how many seconds would it take Barry to walk from one end of the walkway to the other?

A) 48
B) 60
C) 72
D) 75
E) 80


Say Barry's speed is b meter per second and walkaway speed is w meter per second, then as Speed=\frac{Distance}{Time} we'll have that:

b+w=\frac{30}{30}=1;
b-w=\frac{30}{120}=\frac{1}{4};

Sum these two equations; 2b=\frac{5}{4} --> b=\frac{5}{8}.

Time=\frac{Distance}{Speed}=\frac{30}{(\frac{5}{8})}=48.

Answer: A.

Hope it helps.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink] New post 09 Dec 2012, 21:54
How do we know that it is b-w? Why cant it be w-b. The question never says anything about the speeds of b or w individually.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink] New post 09 Dec 2012, 22:46
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maddyboiler wrote:
How do we know that it is b-w? Why cant it be w-b. The question never says anything about the speeds of b or w individually.


If it is w-b, it means that speed of walkway is more than than his speed, then how will he reach the other end of the walkway.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink] New post 10 Dec 2012, 06:41
Make sense, thanks.
Re: Barry walks from one end to the other of a 30-meter long   [#permalink] 10 Dec 2012, 06:41
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