A flock of swans is sitting peacefully on a pond. Then, suddenly, one of the swans hears something in a bush at the water’s edge, and it takes off and flies away.

Suppose that if swans have flown away, the probability of another swan subsequently joining them is (so the more swans fly, the more likely it is that more swans fly also). What is the probability that the entire flock of swans flies away once the first one takes off?

The solution can be found here. Happy puzzling!

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