Paths dodging a closed intersection

MediumCombinatorics~4m

Moving only right or up on the integer grid, how many lattice paths go from (0,0)(0,0) to (5,4)(5,4) without passing through the point (2,2)(2,2)?

Show hints (2)+
  1. Count all paths, then subtract the paths that pass through (2,2)(2,2).
  2. Paths through (2,2)(2,2) factor as (42)⋅(52)\binom{4}{2}\cdot\binom{5}{2}; total is (94)\binom{9}{4}.

Answer

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66

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