Dm:
Distance to the destination after m random walk
steps (with changes)
Dm has a binomial distribution:
for unrestricted range
of distances in both directions
with
mean E(Dm) = D – m (q –p)/(q +p); variance s2(Dm) = mpq/(q +p)
if m(q –p)/(q +p) > D ̃ E(Dm) <
0 ̃ destination is reached with > 50%