rohan2345 wrote:
Jacks watch gains 10 seconds every hour. Jose’s watch loses 15 seconds every 30 minutes. If they set their watches correctly at 10:00 am, after how many hours will the two watches show the same time again?
A- 360 hours
B- 720 hours
C- 1080 hours
D- 1440 hours
E- 2160 hours
Jack's way h gains 10 secs and Jose's loses 15 sec in 30 min or 30 secs in 1 HR..
So the difference in 1 HR is 40 secs..
Now since it is given 10:00 am and asks for the same time again, it means a difference of 24 hrs since we are taking AM in consideration otherwise it would have been 12 hrs..
So if 40sec in 1hr, 24 hour in 24*60*60/40=2160 hrs
Had it been 10:00 to 10:00 that is 12 hrs ana will be 2160/2=1080
But as per the wordings of question Ans should be 2160..
_________________
1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
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31% (01:38) correct 
