Find all School-related info fast with the new School-Specific MBA Forum
Learn more about the recent changes... close

It is currently 24 May 2013, 13:05
Customize  |  Hide

Search
Register
New posts
Unanswered

Not a tough one, but tricky enough to share it... There are

  Question banks Downloads My Bookmarks Reviews  
  Oldest Best Reply
Search for:
 
Print view
First unread post
Author Message
TAGS:
Senior Manager
Senior Manager
Joined: 15 Aug 2007
Posts: 257
Schools: Chicago Booth
Followers: 1

Kudos [?]: 36 [0], given: 0

GMAT Tests User
Not a tough one, but tricky enough to share it... There are [#permalink] New post 19 Mar 2008, 11:36
00:00

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Not a tough one, but tricky enough to share it...

There are many taps in the pool. One tap can fill the pool in 50 hours. Someone opens the first tap and further opens a new tap each following hour. In approximately how many hours the pool will be filled?

(A) 6
(B) 8
(C) 9
(D) 10
(E) 12
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3596
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 231

Kudos [?]: 1300 [0], given: 346

GMAT ToolKit User GMAT Tests User
Re: PS: Taps [#permalink] New post 19 Mar 2008, 12:19
D

1 hour: rate=1/50
2 hour: rate=2*1/50
n hour: rate=n*1/50

1=1/50+2/50+...+n/50=n*(n+1)/(2*50)

n^2+n=100

if n=9 then n^2+n=90<100: the pool is not filled
if n=10 then n^2+n=110>100: the pool is filled

Therefore, we need 10 hours

P.S. we can find precise time that will be equal 9.5 hours
but if we had got 9.45 hours, what option would we have preferred?
I would have chosen 10 hours because at 9 hours we have got unfilled pool. Any thoughts?
_________________

iOS/Android: GMAT ToolKit - The bestselling GMAT prep app | GMAT Club (free) | PrepGame | GRE ToolKit | LSAT ToolKit
PROMO: Are you an exiting GMAT ToolKit (iOS) user? Get GMAT ToolKit 2 (iOS) for only $0.99 (read more)
Math: GMAT Math Book ||| General: GMATTimer ||| Chicago Booth: Slide Presentation
The People Who Are Crazy Enough to Think They Can Change the World, Are the Ones Who Do.

Current Student
Joined: 28 Dec 2004
Posts: 3439
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 11

Kudos [?]: 134 [0], given: 2

GMAT Tests User
Re: PS: Taps [#permalink] New post 19 Mar 2008, 13:56
I get slightly below 10 also..

here is how

after 1st hr=1/50
after 2nd hr=2/50
after 3rd=3/50

so the equation becomes

time to fill= 1/50+2/50+3/50+-....1/50(1+2+3..)=1

plug in u will see that it take about 9.5 hrs..
Senior Manager
Senior Manager
Joined: 15 Aug 2007
Posts: 257
Schools: Chicago Booth
Followers: 1

Kudos [?]: 36 [0], given: 0

GMAT Tests User
Re: PS: Taps [#permalink] New post 20 Mar 2008, 07:56
D is the correct answer indeed.
Manager
Manager
User avatar
Joined: 05 Feb 2007
Posts: 141
Followers: 1

Kudos [?]: 7 [0], given: 7

Re: PS: Taps [#permalink] New post 27 Mar 2008, 21:11
anyone else with explanations?

I tried doing this: (i'm wondering why this was wrong)

Hour1: 1/50t = 1
Hour2: 2/50t = 49/50
Hour3: 3/50t = 48/50
...
Hour7: 7/50t = 44/50

let t =7 49/50 is greater then 44/50, so pool is filled


Can anyone help me out?
CEO
CEO
User avatar
Joined: 29 Aug 2007
Posts: 2530
Followers: 41

Kudos [?]: 358 [0], given: 19

GMAT Tests User
Re: PS: Taps [#permalink] New post 27 Mar 2008, 22:52
sreehari wrote:
Not a tough one, but tricky enough to share it...

There are many taps in the pool. One tap can fill the pool in 50 hours. Someone opens the first tap and further opens a new tap each following hour. In approximately how many hours the pool will be filled?

(A) 6
(B) 8
(C) 9
(D) 10
(E) 12


in fact, we need 50 hours of work by all taps.

since each hour a tap is added and each tap's performance can be counted in 1 hour interval, 50 = 1 + 2 + 3 + ......... + n

if n = 9, then sum is 45. if n = 10, then sum is 55.
so it should be between 9 and 10 hours but it cannot be 9. sould be approx 10.
_________________

Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Intern
Intern
User avatar
Joined: 04 May 2004
Posts: 49
Location: India
Followers: 0

Kudos [?]: 6 [0], given: 0

Re: PS: Taps [#permalink] New post 27 Mar 2008, 23:29
I have a different way of thinking (trying not to use any math formulas)

End of Hour 1: 1 tap for 1 hour -> 1/50
End of Hour 2: Hour 1 + 2 taps for 1 hour -> 1/50 + 2/50 = 3/50
End of Hour 3: Hour 2 + 3 taps for 1 hour -> 3/50 + 3/50 = 6/50
End of Hour 4: Hour 3 + 4 taps for 1 hour -> 6/50 + 4/50 = 10/50
End of Hour 5: Hour 4 + 5 taps for 1 hour -> 10/50 + 5/50 = 15/50
End of Hour 6: Hour 5 + 6 taps for 1 hour -> 15/50 + 6/50 = 21/50
Hour 7 -> 28/50
Hour 8 -> 36/50
Hour 9 -> 45/50
Hour 10 -> 55/50 overflow ..

Hence hour 10.
_________________

http://twitter.com/Saurabh

Manager
Manager
User avatar
Joined: 05 Feb 2007
Posts: 141
Followers: 1

Kudos [?]: 7 [0], given: 7

Re: PS: Taps [#permalink] New post 28 Mar 2008, 16:47
thanks guys...all clear...stupid mistake
CEO
CEO
User avatar
Joined: 29 Aug 2007
Posts: 2530
Followers: 41

Kudos [?]: 358 [0], given: 19

GMAT Tests User
Re: PS: Taps [#permalink] New post 28 Mar 2008, 18:46
GMAT TIGER wrote:
sreehari wrote:
Not a tough one, but tricky enough to share it...

There are many taps in the pool. One tap can fill the pool in 50 hours. Someone opens the first tap and further opens a new tap each following hour. In approximately how many hours the pool will be filled?

(A) 6
(B) 8
(C) 9
(D) 10
(E) 12


in fact, we need 50 hours of work by all taps.

since each hour a tap is added and each tap's performance can be counted in 1 hour interval, 50 = 1 + 2 + 3 + ......... + n

if n = 9, then sum is 45. if n = 10, then sum is 55.
so it should be between 9 and 10 hours but it cannot be 9. sould be approx 10.


Small edit: hours should be tapes. since 9 and a fraction tapes are not possible. so it must be 10 tapes even if the no. of tapes comes as 9.01.
so it is 10 taps.
_________________

Verbal: new-to-the-verbal-forum-please-read-this-first-77546.html
Math: new-to-the-math-forum-please-read-this-first-77764.html
Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Re: PS: Taps   [#permalink] 28 Mar 2008, 18:46
    Similar topics Author Replies Last post
Similar
Topics:
 New posts this is the tricky one so I thought to share with u all.. tarungmat 5 04 Jun 2005, 13:22
New posts tricky one sharadGmat 5 25 Jun 2006, 02:08
Popular new posts tricky one sharadGmat 11 25 Jun 2006, 02:15
This topic is locked, you cannot edit posts or make further replies. New EXPERTS_POSTS_IN_THIS_TOPIC Tough and tricky 2: Bunuel 4 11 Oct 2009, 17:17
New posts EXPERTS_POSTS_IN_THIS_TOPIC Tough and tricky 5: Race Bunuel 5 11 Oct 2009, 18:14
Display posts from previous: Sort by

Not a tough one, but tricky enough to share it... There are

  Question banks Downloads My Bookmarks Reviews  
Print view
First unread post

Moderators: Bunuel, VeritasPrepKarishma, IanStewart

Search for:


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.

Main navigation

GMAT Resources

Partners

MBA Resources

www.gmac.com|www.mba.com