The only timepiece that Mr. Greenwich owns is a grandfather clock which he frequently forgets to wind.
One day when this happened, he went to Mr. Terminal's house to check the time. When Mr. Greenwich returned home, the first thing he did was set his grandfather clock to the correct time.
How could he correctly set his clock if he did not know the length of the trip to Mr. Terminals house?
Note: he did not use a radio or telephone etc. to aid him.
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When Mr. Greenwich left his house he wound the clock and noted the time. When he returned, the grandfather clock told him the amount of time he took walking to Mr. Terminal's house, visiting, and returning home. Mr. Greenwich also noted his arrival and departure time at Mr. Terminal's so he was able to tell how much time he spent there. He then subtracted this amount of time from the total time he was away from home, (as measured by his grandfather clock). This amount of time is how long he spent walking to Mr. Terminal's house and back. Since he always walks the same way and at the same speed, half of his travel time was the time spent walking home. He then added this time to the time he noted leaving Mr. Terminal and that gave him the correct time of his arrival home.
