coins are flipped randomly by Bob, and then placed in a line.
For an arrangement of coins , suppose is a subset of consecutive elements of (meaning that they appear next to each other in the line). Let and be the number of coins facing up and down in , respectively. is considered to be if for any , .
Given that an arrangement is , what is the probability that it is also ? Express your answer as where and are relatively prime natural numbers. What is ?
Tip: There's a nice, simple way to solve this without casework. Don't make things too complicated!
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