A one-dimensional random walker takes steps to left or right with equal probability. The probability that the random walker starting from origin is back to origin after N even number of steps is
A. $$\frac{{N!}}{{\left( {\frac{N}{2}} \right)!\left( {\frac{N}{2}} \right)!}}{\left( {\frac{1}{2}} \right)^N}$$
B. $$\frac{{N!}}{{\left( {\frac{N}{2}} \right)!\left( {\frac{N}{2}} \right)!}}$$
C. $$2N!{\left( {\frac{1}{2}} \right)^{2N}}$$
D. $$N!{\left( {\frac{1}{2}} \right)^N}$$
Answer: Option A
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