AQuA-RAT train #53249 · Combinatorics · Permutations & combinations

There are 20 people among whom two are sisters

There are 20 people among whom two are sisters. Find the number of ways in which we can arrange them around a circle so that there is exactly one person between the two sisters ?

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AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #53249

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