Found problems: 401
2024 OMpD, 3
A confused cockroach is initially at vertex $A$ of a cube $ABCDEFGH$ with edges measuring $1$ meter, as shown in the figure. Every second, the cockroach moves $1$ meter, always choosing to go to one of the three adjacent vertices to its current position. For example, after $1$ second, the cockroach could stop at vertex $B$, $D$, or $E$.
(a) In how many ways can the cockroach stop at vertex $G$ after $3$ seconds?
(b) Is it possible for the cockroach to stop at vertex A after exactly $2023$ seconds?
(c) In how many ways can the cockroach stop at A after exactly $2024$ seconds?
Note: One way for the cockroach to stop at a vertex after a certain number of seconds differs from another way if, at some point, the cockroach is at different vertices in the trajectory. For example, there are $2$ ways for the cockroach to stop at $C$ after $2$ seconds: one of them passes through $A$, $B$, $C$, and the other through $A$, $D$, $C$.
[img]https://cdn.discordapp.com/attachments/954427908359876608/1299721377124847616/Screenshot_2024-10-16_173123.png?ex=671e3b5b&is=671ce9db&hm=76962ee2949d8324c2f7022ef63f8b7d3c6fe3aabf4ecf526f44249439f204ac&[/img]