Hot water and Cold Water tubes

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Hot water and Cold Water tubes

by ramyaravindran » Thu Jul 16, 2009 6:12 am
Searched this forum but could not find this question answered before. Can someone help explain the OA.

A cold water tube can fulfill a pool in C hours; a hot water tube can fulfill it in H hours. C<H. Two tubes together can fulfill the pool in T hours. Which of the following must be true?
I. 0<T<H
II. C<T<H
III. C/2 < T < H/2

OA: I + III

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by shibal » Thu Jul 16, 2009 6:22 am
The easier way (IMO) is to plug in numbers. So if C=2 and H=4 (C<H) T will be 4/3 (1/2+1/4=1/T)... Just check with the options and u'll see that I and III are the ones that must be true

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by ramyaravindran » Thu Jul 16, 2009 6:27 am
Thanks Shibal.

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by abhinav85 » Thu Jul 16, 2009 10:25 am
IMO 1&3
Last edited by abhinav85 on Thu Jul 16, 2009 11:22 am, edited 1 time in total.

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by kaulnikhil » Thu Jul 16, 2009 11:17 am
1/2 +1/3 = 1/t
5/6 = 1/t
t =6/5 = 1.2
1<1.2<1.5
still satisfies III

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by Ian Stewart » Thu Jul 16, 2009 11:37 am
If you want to understand why I and III must be true here (for any numbers), I posted an explanation here:

www.beatthegmat.com/rates-problem-t21746.html
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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