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# A not-so-good clockmaker has four clocks on display in the

Author Message
GMAT Instructor
Joined: 07 Jul 2003
Posts: 750
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jul 2003, 05:23
2
18
00:00

Difficulty:

95% (hard)

Question Stats:

36% (02:54) correct 64% (02:03) wrong based on 265 sessions

### HideShow timer Statistics

A not-so-good clockmaker has four clocks on display in the window. Clock #1 loses 15 minutes every hour. Clock #2 gains 15 minutes every hour relative to Clock #1 (i.e., as Clock #1 moves from 12:00 to 1:00, Clock #2 moves from 12:00 to 1:15). Clock #3 loses 20 minutes every hour relative to Clock #2. Finally, Clock #4 gains 20 minutes every hour relative to Clock #3. If the clockmaker resets all four clocks to the correct time at 12 noon, what time will Clock #4 display after 6 actual hours (when it is actually 6:00 pm that same day)?

(A) 5:00
(B) 5:34
(C) 5:42
(D) 6:00
(E) 6:24

OPEN DISCUSSION OF THIS QUESTION IS HERE: a-not-so-good-clockmaker-has-four-clocks-on-display-in-the-w-122994.html

_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

GMAT Instructor
Joined: 07 Jul 2003
Posts: 750
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jul 2003, 06:52
D. is NOT correct. Hint: Say you buy stock for X amount. It then falls by 25%, then subsequently rises by 25%, do you get back to the same place?
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Manager
Joined: 08 Apr 2003
Posts: 143
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jul 2003, 09:47
Hi,

I answer i got, is 324 minutes that is 5:24.

Now, i am doubtful about the options.

Can you through more light on that...
GMAT Instructor
Joined: 07 Jul 2003
Posts: 750
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jul 2003, 12:33
7
2
The correct answer is (A). Clock #1 is 15 minutes slow. This means that after one actual hour, the clock shows that only 45 minutes have gone by.

Clock #2 is 15 minutes fast relative to Clock #1. That means that after one hour on Clock #1, Clock #2 moves ahead 60 + 15 or 75 minutes. This ALSO means that Clock #2 is running 75/60 = 5/4 times as fast as Clock #1. Therefore, after one actual hour of elapsed time, Clock #1 moves 45 minutes and Clock #2 moves 45 * 5/4 minutes.

Clock #3 is 20 minutes slow relative to clock one. That means that after one hour on Clock #2, Clock #3 moves ahead 60 - 20 or 40 minutes. This ALSO means that Clock #3 s running 40/60 = 2/3 times as fast as Clock #2. Hence, after one actual hour of elapsed time, Clock #1 moves 45 minutes, Clock #2 moves 45 * 5/4 minutes, and Clock #3 moves 45 * 5/4 * 2/3 minutes.

Clock #4 is 20 minutes fast relative to Clock #3. That means that after one hour on Clock #3, Clock #4 moves ahead 60 + 20 or 80 minutes. This ALSO means that Clock #4 is running 80/60 = 4/3 times as fast as Clock #3. Hence, after one actual hour of elapsed time, Clock #1 moves 45 minutes and Clock #2 moves 45 * 5/4 minutes, Clock #3 moves 45 * 5/4 * 2/3 minutes, and Clock #4 moves 45 * 5/4 * 2/3 * 4/3 = 50 minutes which is equivalent to saying that Clock #4 loses 10 minutes per actual hour.

At 6 p.m., six actual hours have gone by since all of the clocks were reset, hence Clock #4 loses 6 * 10 = 60 minutes, i.e., Clock #4 is an hour slow. Hence, the apparent time on Clock #4 is 5:00 p.m. and the correct answer is (A).
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Manager
Joined: 08 Apr 2003
Posts: 143
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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08 Jul 2003, 04:40
Hey, i just learnt my mistake here...

I was calculating it as 125/100*80/100*120/100(time lost by clock 1).

The base chosen was wrong. I used 100 as base instead of 60. Ooops...!!!

Well thanks Akamaibrah.... for a lovely problem.
CEO
Joined: 15 Aug 2003
Posts: 3377
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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06 Jan 2004, 23:13
A not-so-good clockmaker has four clocks on display in the window. Clock #1 loses 15 minutes every hour. Clock #2 gains 15 minutes every hour relative to Clock #1 (i.e., as Clock #1 moves from 12:00 to 1:00, Clock #2 moves from 12:00 to 1:15). Clock #3 loses 20 minutes every hour relative to Clock #2. Finally, Clock #4 gains 20 minutes every hour relative to Clock #3. If the clockmaker resets all four clocks to the correct time at 12 noon, what time will Clock #4 display after 6 actual hours (when it is actually 6:00 pm that same day)?

(A) 5:00
(B) 5:34
(C) 5:42
(D) 6:00
(E) 6:24

Intern
Joined: 22 Nov 2003
Posts: 40
Location: Serbia
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jan 2004, 07:40
5
1

Let me expound:

Afer six actual hours :

I clock: after six hours , the first clock displayed 4:30, because it lost 6 x 15 min = 90 min. Thus 6:00 - 1:30 =4:30

II clock gains 15 min per hour relative to Clock 1. It gained 15 x 4.5 = 67,5 minutes. => Clock 2 displayed 4:30:00 +1:07:30 = 5 hous 37 minutes and 30 seconds.
III clock: its loss relative to Clock 2 was 5 x 20 + (37,5 / 60) x 20= 100 +0,625 x 20=112,5 minutes. => 5:37:30 -1:52:30 = 3:45

Finally : Clock # 4 - gained 3 x 20 + 0,75 x 20 = 1 h 15 min => 3:45 +1:15 = 5:00 => A
Senior Manager
Joined: 05 May 2003
Posts: 412
Location: Aus
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jan 2004, 07:45
Even I found the answer to be A. Is this a GMAT problem ? I took more than five mins to solve this rather understand this.
CEO
Joined: 15 Aug 2003
Posts: 3377
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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07 Jan 2004, 18:03
Geethu wrote:
Even I found the answer to be A. Is this a GMAT problem ? I took more than five mins to solve this rather understand this.

this is a MGMAT problem
SVP
Joined: 30 Oct 2003
Posts: 1737
Location: NewJersey USA
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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26 Jan 2004, 13:17
3
2
6 * ( 1-1/4) (1+1/4)(1-1/3)(1+1/3)
1/4 hr is 15 minutes and 1/3 hr is 20 minutes

6 * ( 1-1/16) * ( 1-1/9 ) = 6 * 15/16 * 8/9 = 6 * 5/6 = 5
Sothe 4th clock should just display 5 hrs after 12
Manager
Joined: 03 Feb 2015
Posts: 50
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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25 Feb 2015, 13:22
why did you post this in sub 600
Non-Human User
Joined: 09 Sep 2013
Posts: 9464
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

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04 Aug 2018, 07:02
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A not-so-good clockmaker has four clocks on display in the &nbs [#permalink] 04 Aug 2018, 07:02
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