at 9 a.m. a man starts hiking a path up a Hill . he walks at a variable pace, resting occasionally, but never actually reversing his direction. at 9 p.m. he reaches the top. he camps out overnight. the next morning he wakes up at 9 a.m. and starts his descent down the Hill . again he walks down the path at a variable pace, resting occassionally, but always going downhill. at 9 p.m. he reaches the bottom. what is the probability that at some time during the second day, he is in the exact same spot he was in on the first day?