# Solution #88: One Clock

He wound his clock and set it at some particular time before he left. He
noted the exact time of his arrival at and departure from his friend's house.
He noted the time showing on his clock when he returned. He walked at the same
pace on the two journeys. The elapsed time on his clock is the duration of the
two journeys plus the length of his visit to his friend. Knowing the time he
spent with his friend, he subtracts this from the elapsed time on his clock and
divides the result by two in order to calculate the duration of the journey.
He adds this to the exact time he left his friend's house in order to set his
clock at the correct time. For example, assume he set his clock at 12, arrived
at his friend's at 6:30, and left at 7:30. When he returned, his clock showed
4:00. Then his journey took one and one half hours and the correct time is
9:00.

Source: Sloane, Paul

Categories: Reasoning, Process, Algebra

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