Although I am sure that my watch is 5 minutes fast, in reality it is 10 minutes slow. On the other hand, my friend's watch is actually 5 minutes fast, although he thinks his watch is correct. We made an appointment to meet at 10 o'clock and plan to arrive punctually. Who will arrive first? How long after will the other arrive?
I will arrive when my watch reads 10:05, as I think my watch is five minutes fast. Since it is actually ten minutes slow, I will actually arrive at 10:15. My friend will arrive when his watch reads 10:00, as he thinks his watch is correct, but in reality, it will be 09:55. Therefore, my friend will arrive twenty minutes before me.