Although I am certain that my watch is 5 minutes fast, it is actually 10 minutes slow. On the other hand, my friend's watch is actually 5 minutes fast, although he thinks it is correct. We made a plan to meet at 10 o'clock and intend to arrive punctually. Who will arrive first? How long after will the other arrive?
I will arrive when my watch reads $10 \mathrm{~h} 5 \mathrm{~min}$, thinking that my watch is fast by $5 \mathrm{~min}$. Since it is actually slow by $10 \mathrm{~min}$, I will actually arrive at $10 \mathrm{~h} 15 \mathrm{~min}$.

My friend will arrive when his watch reads 10 hours, thinking that his watch is correct, but in reality it will be $9 \mathrm{~h} 55 \mathrm{~min}$. Therefore, my friend will arrive 20 minutes before me.