4. In this time-line of John going up and down a mountain, tell a reasonable time when John might be in the same place at the same time of day. Mark it on the time-line:
5. Explain how we know that if Mark hikes from the bottom of the mountain to the top between 1 pm and 8 pm on Monday, and he hikes from the top of the mountain to the botton between 1 pm and 8 pm on Tuesday, there must be at least one time between 1 and 8 that he is at the same height of the mountain on both days.