Absorption probability on a line

A token sits at position 22 on {0,1,2,3,4}\{0,1,2,3,4\}. Each step it moves ±1\pm 1 with equal probability; 00 and 44 are absorbing. What is the probability it is absorbed at 44? (to 3 decimals)

Show hints (2)+
  1. Absorption probability is harmonic, hence linear, in position.
  2. P=(start)/(right barrier)P = (\text{start})/(\text{right barrier}).

Answer

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0.5 (± 0.005)

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