At home we have three watches. On January 1, all of them marked the correct time, but only one of them worked precisely. Another one was late 1 minute per day and the third one was ahead 1 minute daily.
After how long will the three clocks re-mark the exact time?
After 720 days the three will mark the correct time again. At this time, the clock ahead will mark the correct time, the clock that is delayed 720 minutes, that is 12 hours will mark the correct time again and the last clock will mark the correct time since it works well. Therefore, the three clocks will mark the exact time on January 1 two years after the first time.