You have the misfortune to own an unreliable clock. This one loses exactly 10 minutes every hour. It is now showing 5:00am and you know that is was correct at midnight, when you set it. The clock stopped 8 hours ago, what is the correct time now?
The clock is losing 10 minutes every hour, so for every real hour that has passed, the clock will only show 50 minutes.
The clock now shows 5:00am, so we know that 300 clock minutes have passed. As every 50 clock minutes is actually a real hour: 300 ÷ 50 = 6 hours. So the clock stopped at 6:00am.
As the clock stopped 8 hours ago, the time now must be 2.00pm. QED.