You have the misfortune to own an unreliable clock. This one gains exactly 18 minutes every hour. It is now showing 1:00pm and you know that is was correct at midnight, when you set it. The clock stopped 12 hours ago, what is the correct time now?

**Answer:** 10.00pm.

Since the clock is gaining 18 minutes every hour, for every real hour that has passed, the clock will show 78 minutes. Since the clock shows 1.00pm, we know that 780 clock minutes have passed. This therefore equals 600 real minutes and hence 10 hours. The clock stopped 720 minutes ago, therefore the time must now be 10.00am. QED.