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MathNet 2021 — Part 10 Question 7

Math Olympiad Vault · MathNet 2021 — Part 10

Question 7

A bug starts at a vertex of a grid made up of equilateral triangles of side length $1$. At each step the bug moves in one of the $6$ possible directions along the grid lines randomly and independently with equal probability. What is the probability that after $5$ moves the bug never will have been more than $1$ unit away from the starting position?
  1. $\frac{13}{108}$
  2. $\frac{7}{54}$
  3. $\frac{29}{216}$
  4. $\frac{4}{27}$
  5. $\frac{1}{6}$