GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 14 Dec 2019, 02:47

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Senior Manager
Senior Manager
avatar
Status: Finally Done. Admitted in Kellogg for 2015 intake
Joined: 25 Jun 2011
Posts: 439
Location: United Kingdom
Concentration: International Business, Strategy
GMAT 1: 730 Q49 V45
GPA: 2.9
WE: Information Technology (Consulting)
A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 10 Nov 2011, 16:15
9
42
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

39% (03:18) correct 61% (02:49) wrong based on 329 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

_________________
Best Regards,
E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610
GMAT ==> 730
Most Helpful Expert Reply
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 9876
Location: Pune, India
Re: Clockmaker  [#permalink]

Show Tags

New post 10 Nov 2011, 23:19
31
1
23
enigma123 wrote:
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

Guys - again the official answer is not provided. But I have done the Maths to get D. Do you think D is the right answer? Can someone explain to me if you think D is not the right answer?


Here is my approach to such problems:

1. Loses 15 mins every hour (i.e. 60 mins) means the clock's speed is a fourth less than the normal speed. So the clock's speed is (3/4)th the normal speed. It covers only 45 mins in the time in which a correct clock covers 60 mins.
2. Gains 20 mins every hour means the clock's speed is a third more than normal speed. So the clock's speed is (4/3) times the normal speed. It covers 1 hr 20 mins in the time in which a correct clock covers 1 hr.

Let speed of a correct clock = s
Speed of clock 1 = (3/4)s
Speed of clock 2 = (3/4)s * (5/4) = (15/16)s
Speed of clock 3 = (15/16)s * (2/3) = (5/8)s
Speed of clock 4 = (5/8)s * (4/3) = (5/6)s

Speed of the fourth clock is (5/6)th the normal speed. If a correct covers 6 hrs, the fourth clock will cover 5 hrs. Hence, the time shown will be 5:00 pm
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Most Helpful Community Reply
Manager
Manager
avatar
Joined: 20 Aug 2011
Posts: 103
Re: Clockmaker  [#permalink]

Show Tags

New post 10 Nov 2011, 22:09
8
5
C1 loses 15 minutes every hour. So after 60 minutes have passed, C1 displays that 60-15 = 45 minutes have passed.

C2 gains 15 minutes for every 60 minutes displayed on C1. Thus, the time displayed on C2 is 75/60 = 5/4 the time displayed on C1. So after 60 minutes have passed, C2 displays the passing of (5/4 * 45) minutes.

C3 loses 20 minutes for every 60 minutes displayed on C2. Thus, the time displayed on C3 is 40/60 = 2/3 the time displayed on C2. So after 60 minutes have passed, C3 displays the passing of (2/3 * 5/4 * 45) minutes.

C4 gains 20 minutes for every 60 minutes displayed on C3. Thus, the time displayed on C4 is 80/60 = 4/3 the time displayed on clock 3. So after 60 minutes have passed, C4 displays the passing of 4/3 * 2/3 * 5/4 * 45 = 50 minutes.

C4 loses 10 minutes every hour.
In 6 hours, C4 will lose 6*10 = 60 minutes = 1 hour.
Since the correct time after 6 hours will be 6pm, C4 will show a time of 6-1 = 5pm.

The correct answer is A.
General Discussion
Senior Manager
Senior Manager
avatar
Joined: 28 Jul 2011
Posts: 295
Location: United States
Concentration: International Business, General Management
GPA: 3.86
WE: Accounting (Commercial Banking)
Re: Clockmaker  [#permalink]

Show Tags

New post 11 Nov 2011, 21:40
Good explanation.......:)
Senior Manager
Senior Manager
User avatar
B
Joined: 11 May 2011
Posts: 284
Re: Clockmaker  [#permalink]

Show Tags

New post 12 Nov 2011, 13:48
1
Here is my take on this question. My answer is D.
I'll solve this with examples. Below is the movement of each cocks based on 12:00 noon as a reference.

Clock #1 moves from 12:00 to 1:00
Clock #2 moves from 12:00 to 1:15
Clock #3 moves from 12:00 to 12:55
Clock #4 moves from 12:00 to 1:15
Note - movement of Clock #2 and Clock #4 are same that makes life easier.

Time in each Clock at actual 6:00 pm that same day -
Clock #1 moves from 12:00 to 4:30
Clock #2 moves from 12:00 to 6:00
Clock #3 moves from 12:00 to 12:55 (Desb't matter)
Clock #4 moves from 12:00 to 6:00

Based on the calculation above. My answer is D.
Cheers!
_________________
-----------------------------------------------------------------------------------------
What you do TODAY is important because you're exchanging a day of your life for it!
-----------------------------------------------------------------------------------------
Senior Manager
Senior Manager
avatar
Status: Finally Done. Admitted in Kellogg for 2015 intake
Joined: 25 Jun 2011
Posts: 439
Location: United Kingdom
Concentration: International Business, Strategy
GMAT 1: 730 Q49 V45
GPA: 2.9
WE: Information Technology (Consulting)
Re: Clockmaker  [#permalink]

Show Tags

New post 12 Nov 2011, 14:41
Thanks Capricorn369. Please see explanation from Karishma and Blink 005. Answer is A.
_________________
Best Regards,
E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610
GMAT ==> 730
Manager
Manager
User avatar
Status: livin on a prayer!!
Joined: 12 May 2011
Posts: 102
Location: Australia
Re: Clockmaker  [#permalink]

Show Tags

New post 12 Nov 2011, 18:01
My way is identical to Karishma's.
(1) 3/4 speed
(2) 4/3 speed

let s = speed of clock
1) 3/4s
2) (3/4)(5/4)s = 15/16s
3) (15/16)(2/3)s = 5/8s
4) (5/8)(4/3)s = 5/6s

so 5/6s * 6 = 5 o'clock
2
Senior Manager
Senior Manager
User avatar
B
Joined: 11 May 2011
Posts: 284
Re: Clockmaker  [#permalink]

Show Tags

New post 12 Nov 2011, 18:02
enigma123 wrote:
Thanks Capricorn369. Please see explanation from Karishma and Blink 005. Answer is A.


@enigma123 - Thanks for responding. My assumption were incorrect and i'm convinced that answer should be A.
Cheers!
_________________
-----------------------------------------------------------------------------------------
What you do TODAY is important because you're exchanging a day of your life for it!
-----------------------------------------------------------------------------------------
Retired Moderator
User avatar
Joined: 20 Dec 2013
Posts: 166
Location: United States (NY)
GMAT 1: 640 Q44 V34
GMAT 2: 710 Q48 V40
GMAT 3: 720 Q49 V40
GPA: 3.16
WE: Consulting (Venture Capital)
GMAT ToolKit User Reviews Badge
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 16 Jun 2014, 19:07
cleverly written problem, I was also confused by the (i.e., as Clock #1 moves from 12:00 to 1:00, Clock #2 moves from 12:00 to 1:15), as this seems to indicate that Clock #2 properly offsets Clock #1's 15min/hr loss and displays the the real time

however, the 15 minutes clock 1 loses is relative to an hour of real time and not an hour of clock 1's distorted time. So when it reads 1:00 on clock 1, it is not 1:15 in real time, but rather 1:20 --> RT/C1 = (1m)/(3/4m) --> RT = C1(4/3)

So for D to be correct, it would have to read something like as Clock #1 moves from 12:00 to 12:45, Clock #2 moves from 12:00 to 1, etc etc
_________________
Manager
Manager
avatar
Joined: 17 Jul 2013
Posts: 72
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 24 Jul 2014, 03:36
Does such questions appear on actual Gmat test ?
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 9876
Location: Pune, India
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 24 Jul 2014, 04:46
GmatDestroyer2013 wrote:
Does such questions appear on actual Gmat test ?


There is nothing out of the ordinary in this question. It is based on relative speed concepts so you should know how to do it.
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Veritas Prep GMAT Instructor
User avatar
V
Joined: 16 Oct 2010
Posts: 9876
Location: Pune, India
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 30 Nov 2014, 23:48
VeritasPrepKarishma wrote:
enigma123 wrote:
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

Guys - again the official answer is not provided. But I have done the Maths to get D. Do you think D is the right answer? Can someone explain to me if you think D is not the right answer?


Here is my approach to such problems:

1. Loses 15 mins every hour (i.e. 60 mins) means the clock's speed is a fourth less than the normal speed. So the clock's speed is (3/4)th the normal speed. It covers only 45 mins in the time in which a correct clock covers 60 mins.
2. Gains 20 mins every hour means the clock's speed is a third more than normal speed. So the clock's speed is (4/3) times the normal speed. It covers 1 hr 20 mins in the time in which a correct clock covers 1 hr.

Let speed of a correct clock = s
Speed of clock 1 = (3/4)s
Speed of clock 2 = (3/4)s * (5/4) = (15/16)s
Speed of clock 3 = (15/16)s * (2/3) = (5/8)s
Speed of clock 4 = (5/8)s * (4/3) = (5/6)s

Speed of the fourth clock is (5/6)th the normal speed. If a correct covers 6 hrs, the fourth clock will cover 5 hrs. Hence, the time shown will be 5:00 pm


Responding to a pm:

Quote:
how did you get (5/4) for the speed of clock 2?

I understand that clock 1 looses 15 min every hour hence 3/4s
Clock 2 gains 20 mins every hour . hence 4/3 s ?


We are given that "Clock #2 gains 15 minutes every hour relative to Clock #1"

This means that if the speed of clock 1 is s1, the speed of clock 2 is s1 + s1/4 (i.e. clock 2 covers 15 extra mins for every 60 mins covered by clock 1). This gives us that speed of clock 2 is 5s1/4.

Since the speed of clock 1 itself is 3s/4, the speed of clock 2 will be (5/4)*(3s/4) = 15s/16
_________________
Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
Intern
Intern
avatar
Joined: 04 Jul 2015
Posts: 2
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 09 Nov 2015, 03:55
Hi all can ull help me in clarifying this doubt?
I think for clock 1: is losing 15 min means it will show 45 min instead of 1hr but for clock 2 which given in relation with with and mentioned in the question as well it is 15 min ahead of clock 1 and not the real time.
So inf the question mentioned as (clock #1 moves from 12:00 to 12:45,clock2# moves from 12:00 to 1:00) this example considers actual 1 hour

Questionz example (clock#1 moves from 12:00 to 1:00, clock2# from from 12:00 to 1.15) this shows that actual for clock 1 is 1.15 as it loses 15 min every hour and thus implies clock 2 is on time.

Same logic for clock 3 & 4

Hence practically ans marked as A could be a miss print, since we never consider the probability of a miss print, leaving clock 4 # with ans D in opinion.

Please clarify if i have missed any point?
VP
VP
avatar
P
Joined: 07 Dec 2014
Posts: 1217
A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 09 Nov 2015, 20:54
60 minutes x [(3/4)(5/4)(2/3)(4/3)]=60(5/6)=50 minutes
clock 4 loses 10 minutes per hour➡1 hour per 6 hours
at actual 6:00pm clock 4 will show 5:00pm
Intern
Intern
avatar
Joined: 20 Sep 2016
Posts: 2
GMAT ToolKit User
Re: A not-so-good clockmaker has four clocks on display in the w  [#permalink]

Show Tags

New post 18 Nov 2016, 00:21
1
1
Actual time 06:00 pm

Clock 1 (losses 15 mins/hr relative to actual time) shows : 04:30 pm

Clock 2 (gains 15 mins/hr relative to clock 1) shows : 04:30 pm + (4x15 + (15/2) = 67.5 mins) = 05:37.5 pm

Clock 3 (losses 20 mins/hr relative to clock 2) shows : 05:37.5 pm - (5x20 + [(1/3)x37.5= 12.5] = 112.5 mins) = 03:45 pm

Clock 4 (gains 20 mins/hr relative to clock 3) shows : 03:45 + (3x20 + [(1/3)x45= 15] = 75 mins) = 05:00 pm

Winkherehere :!:
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 13741
Re: A not-so-good clockmaker has four clocks on display in the  [#permalink]

Show Tags

New post 21 Aug 2019, 00:07
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).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Club Bot
Re: A not-so-good clockmaker has four clocks on display in the   [#permalink] 21 Aug 2019, 00:07
Display posts from previous: Sort by

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





cron

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne