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..
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GMAT Expert

Jacks watch GAINS 10 seconds every HOUR.

Jose’s watch loses 15 seconds every 30 minutes
This means Jose’s watch LOSES 30 seconds every HOUR

In 1 HOUR, the time difference between the two watches is 40 seconds
So, in 2 HOURS, the time difference between the two watches is 80 seconds
So, in 3 HOURS, the time difference between the two watches is 120 seconds
Or we can say:, in 3 HOURS, the time difference between the two watches is 2 MINUTES
So, in 90 HOURS, the time difference between the two watches is 60 MINUTES
In other words, in 90 HOURS, the time difference between the two watches is 1 HOUR

KEY CONCEPT: In order for their watches to show the same time, we need a time difference of 24 HOURS
We know that, in 90 HOURS, the time difference between the two watches is 1 HOUR

Multiple both values by 24 to get: in 2160 HOURS, the time difference between the two watches is 24 HOURS

Answer: E

Cheers,
Brent
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