128.Charlie Between Two Boys
★★★classical probabilityCh. 1 — Classical Probability and Combinatorics444+ Problems in Probability
There are 14 boys standing in a circle, one of whom is Charlie. 10 girls walk up and join the circle at random to form a larger circle, and each girl must stand between 2 boys. If all ways of forming the larger circle are equally likely, find the probability that Charlie is still standing between two boys.
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The girls occupy 10 of the 14 gaps between adjacent boys. Which gaps must stay empty for Charlie?
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