Explanation:
Time from 6am on Monday to 6pm on following Monday = 7 days and 12 hours, i.e. 24*7 + 12 = 180 hours
So, the watch gains
minutes in 180 hours
Now,
minutes are gained in 180 hours
∴ 5 minutes will be gained in
hours or 83 hours 20 minutes.
83 hour 20 minutes = 3 days (72 hours) 11 hours 20 minutes
Therefore, the watch was correct 3 days 11 hours 20 minutes after 6am on Monday, i.e. it was correct at 20 minutes past 5pm on Thursday.