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

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

Post Wed Sep 20, 2017 7:41 am
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

The OA is A.

What are the calculus that I should do to solve this PS question?

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Post Wed Sep 20, 2017 7:44 am
Quote:
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 B = Barry's rate and W = the walkway's rate.
The distance can be ANY VALUE.
Let the distance = 240 meters.

WITH the walkway, the time = 30 seconds:
Here, Barry and the walkway WORK TOGETHER, so we ADD their rates:
B+W = d/t = 240/30 = 8 meters per second.

AGAINST the walkway, the time = 120 seconds:
Here, the walkway works AGAINST Barry, so we SUBTRACT their rates:
B-W = d/t = 240/120 = 2 meters per second.

Adding together B+W = 4 and B-W = 2, we get:
(B+W) + (B-W) = 8+2
2B = 10
B = 5 meters per second.

Time for Barry alone:
d/r = 240/5 = 48 seconds.

The correct answer is A.

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Thanked by: Vincen
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