“The Stopped Clock”: Solution
Solution to The Stopped Clock:
Before she leaves the house, Andrea winds her own clock and sets it to an arbitary time. Then she notes the correct time at her friend’s house both when she arrives and when she leaves. When she returns home she consults her own clock to see how much time the whole trip has taken, subtracts the period she spent at her friend’s house, and divides the result by two to learn the travel time in each direction. By adding this interval to the time she noted as she left her friend’s house, she can infer the current time and set her own clock.
