gauravnagpal wrote:
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
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