Barry walks from one end to the other of a 30-meter long : GMAT Problem Solving (PS)
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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]

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20 Oct 2012, 09:12
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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]

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20 Oct 2012, 11:55
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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)

=> 2x = 5/4
=> x = 5/8

therefore, 30/x = 48

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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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22 Oct 2012, 06:10
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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; $$2b=\frac{5}{4}$$ --> $$b=\frac{5}{8}$$.

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

Hope it helps.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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09 Dec 2012, 20:54
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]

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09 Dec 2012, 21:46
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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]

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10 Dec 2012, 05:41
Make sense, thanks.
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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31 Dec 2013, 09:03
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

We have 30 (a+b) = 30
a+b = 1

We also get that 120 (a-b) = 30
So a-b = 1

So we have that a = 5/8

So 30*8/5 = 48

Hope it helps!
Cheers

J
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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08 May 2014, 12:57
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Let's try something else JFF ('Just for Fun')

B = Barry's Rate
W= Walkway's

So we have 30 (b+w) = 120 (b-w)
5w = 3b

D=30 (8/5b) = 48b

Time takes for Barry

t = D/R = 48b / b = 48 seconds

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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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20 May 2014, 05:48
Do we actually need to know that the distance is 30 meters?

IF we learn that w=3b/5 we can find distance in terms of 'b' and then divide by rate 'b' to figure out that it will take Ben 48 seconds to reach the end of the walkway

Cheers!
J
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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20 May 2014, 06:03
jlgdr wrote:
Do we actually need to know that the distance is 30 meters?

IF we learn that w=3b/5 we can find distance in terms of 'b' and then divide by rate 'b' to figure out that it will take Ben 48 seconds to reach the end of the walkway

Cheers!
J

No we don't need this value of 30 meters since the distance remains the same while travelling up and down and thus, speeds are inversely proportional to the time taken. The information is superfluous.

Hope it helps!!!
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17 Jun 2015, 15:43
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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26 Jun 2016, 08:30
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Barry walks from one end to the other of a 30-meter long [#permalink]

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26 Jun 2016, 23:36
s1 = 30/30 = 1 metre/sec
s2 = 30/120 = 0.25 metres/sec
now
x+y=1
x-y=0.25
or,
2x=1.25 ==> x = 0.625 metres/sec
and y = 0.375 metres/sec
time taken by barry = 30000/625=48 sec
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Re: Barry walks from one end to the other of a 30-meter long [#permalink]

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21 Nov 2016, 12:28
So basically since barry is moving at a rate and its given that walkway is also moving,thus speed of the walkway must be considered.Right?
Re: Barry walks from one end to the other of a 30-meter long   [#permalink] 21 Nov 2016, 12:28
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