April 2007 IBM Ponder This Challenge

[f97tosc]

Yeah good point, I think the discrepancy boils down to exactly how the frog starts off its epic journey, and that wasn't exactly well defined in the problem statement.

The answer 1-M = 0.5+Y/2 (using your notation here) essentially assumes, as you write, that there (a.s.) exist some lowest integer below which all integers are missed.

But the problem statement says that the frog "is hopping on the integers from minus infinity". So I think that, loosely speaking, rather than thinking of the frog as starting off at some particular integer, we can say that there is no point below which the frog hasn't been when he reaches 0. That is, every point can be treated as k, again using your notation. And then Y is the answer.

[b87lar]

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We can reformulate the problem to the question "what is the probability that the frog will not eventually land on 0, assuming it starts from minus infinity?".

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Hi - sorry for my dimwittedness: can you please explain more in detail (for the slow dude) how one gets to this from the original?
Thanks!

[lastcardcharlie]

Just to be pedantic (it's late), "minus infinity" and "plus infinity" are not integers.