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

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GMAT Instructor
Joined: 07 Jul 2003
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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, 06:23
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Difficulty:

95% (hard)

Question Stats:

34% (02:58) correct 66% (02:03) wrong based on 254 sessions

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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
[Reveal] Spoiler: OA

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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

Kudos [?]: 240 [0], given: 0

GMAT Instructor
Joined: 07 Jul 2003
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Kudos [?]: 240 [0], given: 0

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, 07:52
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?
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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

Kudos [?]: 240 [0], given: 0

Manager
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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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07 Jul 2003, 10:47
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...

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GMAT Instructor
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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, 13:33
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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).
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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

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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08 Jul 2003, 05:40
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.

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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07 Jan 2004, 00:13
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

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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07 Jan 2004, 08:40
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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

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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07 Jan 2004, 08:45
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.

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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07 Jan 2004, 19:03
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

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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26 Jan 2004, 14:17
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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

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Re: A not-so-good clockmaker has four clocks on display in the [#permalink]

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25 Feb 2015, 14:22
why did you post this in sub 600

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Re: A not-so-good clockmaker has four clocks on display in the   [#permalink] 25 Feb 2015, 14:22
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