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Bunuel
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A wall clock gains 2 mins in 12 hrs, while a table clock 14 Jun 2017, 06:21
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anooshehka
Dear Bunuel,

Could you kindly explain the logic behind the following reasoning that you have made (AFter reviewing the question and answer of the same from others I am still confused):

so both to show the same time next wall clock should make 12 hours revolution (12*60=720 minutes), which it would make in 720/8 * 36 hours = 135 days


sincerely,


Anoosheh
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Wall clock moves 8 minutes in every 36 hours. It should move the whole circle, which is 12 hours or 720 minutes. How many 8-minute intervals are in 720 minutes? 720/8 and for each the wall clock needs 36 hours, thus 720/8 * 36 hours = 135 days.
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A wall clock gains 2 mins in 12 hrs, while a table clock 18 Jun 2018, 12:12
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thank you for teaching us how to do this.
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A wall clock gains 2 mins in 12 hrs, while a table clock 19 Oct 2020, 08:58
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Imagine it this way:

Both hands of the clock work on the same clock but in opposite directions. One hand is 3 times faster then the others. There are 4 regions of the clock, each has 6 hours. Luckily we don't need to do calculations to realize that when one hand makes it to the first 6 hours, the other in the opposite direction has made 18 hours, hence they are in the same position now.

so we just have to calculate in how much time the slower hand reaches 6 hours.

6h=60*6 minutes= 360 minutes.
360/2=180 "units of 2 minutes"
180*36h=6480h
6480/24h=27 exact days, meaning that the real time is exactly, what a coincidence, the same, noon
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A wall clock gains 2 mins in 12 hrs, while a table clock 30 Oct 2020, 14:22
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jlgdr
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A wall clock gains 2 mins in 12 hrs, while a table clock loses 2 mins in 36 hrs; both are set right at noon on Tuesday. The correct time when they both show the same time next would be

A. 12.30 night
B. 12 noon
C. 1.30 night
D. 12 night

Show Spoiler
This question has already been discussed no conclusive answer as yet ....
I tried this way but I got stuck ..
since in one minute clock cover = 360/60 = 6 degrees
degree gained by clock in 12 hours = 2 min = 2*6 = 12
simlarly degrees lost by the other clock = 12 degrees
hence after 24 hours ....difference in time .. 8 min = 8*6 = 48 degreses

distance between two hands = 360- 48 = 312 degrees .. ...

time when this distance will be 0 = 312/ 24 = 12 ( complete cycle of watch) i.e it will take complete 12 days to time to be same and hence the time will be 12 noon....

kindly see if this is the correct ...

Source of question : GMAT club ....

Oa - Sorry was not mentioned
regards

This problem tests the concept of relative rates

We have that a wall clack gains 2 min every 12 hours
Another one loses two minutes every 36 hours

First we need to get the rates to be equivalent so multiplying the first by three we get 6 min every 36 hours

Now, if they move 8 min apart in 36 hours, how much will it take them to show the same time. Well one has to imagine that one of the needles is fixed and the other will move 8 min every 36 hours until it makes a whole turn and reaches the same point. That is the basic concept of relative rates. To do so, since it is a wall clock, we will need it to turn a distance equivalent to 12 hours. Now 12*60 = 720 minutes.

So by direct proportionality we get 720*36/8 that is the time it will take in minutes, divide by 60 to get the time in hours. One will get 54 hours

Now since its 54 hours therefore, it will show exactly the same time cause we have no remainder.

So B is our best answer here

Is this clear?

Hope it helps
Cheers!
J :)
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This is the best explanation I can see around. However, I could find a small mistake in your explanation as highlighted above.

Here (720/8) *36 is already in hours so no need to divide it by 60 instead divide it by 24 so that one will get the number of days based on which one can predict the exact time. In this specific question, it is 135 days so it is clear after 135 days exactly at noon they will coincide.

Hope this helps at least a few aspirants. :thumbsup:

Best Regards,
Pradeep.
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A wall clock gains 2 mins in 12 hrs, while a table clock 01 Nov 2020, 20:11
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Bunuel
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Thanks for the question.

A wall clock gains 2 mins in 12 hrs, while a table clock loses 2 mins in 36 hrs; both are set right at noon on Tuesday.The correct time when they both show the same time next would be
a. 12.30 night
b. 12 noon
c. 1.30 night
d. 12 night

A wall clock gains 2 minutes in 12 hours --> gains 6 mins in 36 hours;
A table clock loses 2 minutes in 36 hours;

Relative speed is 6+2=8 minutes in 36 hours (difference in 36 hours), which means that if we consider a table clock to stay still then a wall clock will move 8 minutes in 36 hours, so both to show the same time next wall clock should make 12 hours revolution (12*60=720 minutes), which it would make in 720/8 * 36 hours = 135 days.

So, the correct time when they both show the same time next would be exactly after 135 days at 12 noon.

Answer: B.

Hope it's clear.
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Hi after 135 days, wall clock will show time 9.00 PM (gain 540 minutes) and table clock will show the time 9.00 AM (lag 180 minutes). May be some other way to get the answer.

Please help if I missed something.

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A wall clock gains 2 mins in 12 hrs, while a table clock 10 Nov 2020, 12:46
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Bunuel
martie11
Thanks for the question.



A wall clock gains 2 mins in 12 hrs, while a table clock loses 2 mins in 36 hrs; both are set right at noon on Tuesday.The correct time when they both show the same time next would be
a. 12.30 night
b. 12 noon
c. 1.30 night
d. 12 night

A wall clock gains 2 minutes in 12 hours --> gains 6 mins in 36 hours;
A table clock loses 2 minutes in 36 hours;

Relative speed is 6+2=8 minutes in 36 hours (difference in 36 hours), which means that if we consider a table clock to stay still then a wall clock will move 8 minutes in 36 hours, so both to show the same time next wall clock should make 12 hours revolution (12*60=720 minutes), which it would make in 720/8 * 36 hours = 135 days.

So, the correct time when they both show the same time next would be exactly after 135 days at 12 noon.

Answer: B.

Hope it's clear.
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Hi Bunuel,

Would this mean that no matter what the rates are, the time when the clocks are set or the number of clocks, the time when the clocks would display the same time would be the same as the one at which they were set? I understand this should be the case, as using your approach you are essentially 'fixing' clock 2 in time.

Thanks in advance,
oe
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A wall clock gains 2 mins in 12 hrs, while a table clock 01 Sep 2024, 02:34
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