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# GMAT prep PT1 - rates

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Manager
Joined: 04 Dec 2008
Posts: 101
GMAT prep PT1 - rates [#permalink]

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03 Mar 2009, 07:14
I don't understand why 6 is the answer. Isn't 6 equals to 3 Machine R & 3 Machine S?

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Manager
Joined: 27 May 2008
Posts: 197
Re: GMAT prep PT1 - rates [#permalink]

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03 Mar 2009, 07:32
joyseychow wrote:
I don't understand why 6 is the answer. Isn't 6 equals to 3 Machine R & 3 Machine S?

To complete a work,

Machine type R - 36 hrs
Type S -- 18 hrs
So they both combined together can complete the work in 12 hrs.
1/(1/36 + 1/18) i hope you are clear with this logic. Ok to give some base,

Work = rate/time.

For 1 hrs R can do 1/36 part of work
and S can do 1/18 part of work.

So if they work together, (1/36 + 1/18) they can do 1/12 part of work. So they will take total of 12 hrs to complete the work.

Question says no. of S and R is same and the work has to be completed within 2 hours,

(X/36 + X/18) = 1/2 (since 2 hours)

X = 6. (note X is no. of individual machine types)

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: GMAT prep PT1 - rates   [#permalink] 03 Mar 2009, 07:32
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# GMAT prep PT1 - rates

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