Hi everyone,

Today I came across with this problem :

There is a rabbit on the floor of the stairs. Stairs have 3 steps, Rabbit can jump 1 or 2 steps. What is the probability of going to third step from the floor without visiting second step ?

Yeah I know its very easy to see there are 3 possible ways to go to 3 from the floor :

- floor -> 1 -> 2 -> 3
- floor -> 1 -> 3 ( This is the case we want).
- floor -> 2 -> 3

So the answer must be .

Ok everything seems right. But if we represent this problem as a graph , In first step we must choose between 1 or 2 so the probability to go 1 is equal to . In second step we must choose between 2 or 3 so the probability to go 3 is equal to . So the overall the probability is equal to . Second solution have some differences from the first solution but I couldn't figure out what it is.