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# An escalator is descending at constant speed. A walks down

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Director
Joined: 17 Sep 2005
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An escalator is descending at constant speed. A walks down [#permalink]  30 Jun 2006, 09:13
An escalator is descending at constant speed. A walks down and takes 50 steps to reach the bottom. B runs down and takes 90 steps in the same time as A takes 10 steps. How many steps are visible when the escalator is not operating?

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Brajesh
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Joined: 20 Nov 2005
Posts: 2913
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
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Kudos [?]: 110 [0], given: 0

Brajesh, I think these are not the GMAT questions. These are puzzles that come in infosys' aptitude exam.

But solution to this is 150 steps.

visible steps when not operating = n
escalator speed = s
steps taken by A to reach the bottom = 50
steps taken by B to reach the bottom = 90 + (50 - 10) = 130

When walking down, time taken = (n - 50) / s
When running down, time taken = (n - 130) / s

[(n - 50) / s] : [(n - 130) / s] = 5 : 1
(n - 50) : (n - 130) = 5 : 1
(n - 50) * 1 = (n - 130) * 5
n - 50 = 5n - 650
n - 50 - n + 650 = 5n - 650 - n + 650
4n = 600
n = 150
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Director
Joined: 17 Sep 2005
Posts: 930
Followers: 3

Kudos [?]: 37 [0], given: 0

ps_dahiya wrote:
Brajesh, I think these are not the GMAT questions. These are puzzles that come in infosys' aptitude exam.

But solution to this is 150 steps.

visible steps when not operating = n
escalator speed = s
steps taken by A to reach the bottom = 50
steps taken by B to reach the bottom = 90 + (50 - 10) = 130

When walking down, time taken = (n - 50) / s
When running down, time taken = (n - 130) / s

[(n - 50) / s] : [(n - 130) / s] = 5 : 1
(n - 50) : (n - 130) = 5 : 1
(n - 50) * 1 = (n - 130) * 5
n - 50 = 5n - 650
n - 50 - n + 650 = 5n - 650 - n + 650
4n = 600
n = 150

Yes you are right.
Actually one of my friends is preparing for entrance exams of IT sector and I am helping my friend.
I solved most of the questions.
I found few questions interesting and couldn't help posting here to share with you guys.

This is one of the questions I couldn't solve.

Now also I am not able to understand even after looking at your solution.
Could you please elaborate you approach of solving this problem?

Regards,
Brajesh
Intern
Joined: 26 Jun 2006
Posts: 22
Followers: 0

Kudos [?]: 1 [0], given: 0

I think you have to make certain assumptions for this question. I am also in IT industry, as the question is not clear, usually the test takers are to make assumptions and explain the logic of the assumptions, etc.
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