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Problem snapshot

Alternating W and G
Starts with W, ends with G
Either 3 of each (all unique) or 4 of each (all unique)
Which counts could be possible: I. 36 II. 72 III. 576

Rapid plan

Pattern lock: With alternation and fixed ends, the positions of witches and ghosts are fixed. Only internal permutations matter.
Separate cases; compute fast via slots-permutation.

Case A: 3W and 3G, pattern W G W G W G
W slots = 3 distinct W’s can permute in 3! ways
G slots = 3 distinct G’s can permute in 3! ways
Total = 3! * 3! = 6 * 6 = 36 → I is possible

Case B: 4W and 4G, pattern W G W G W G W G
W slots = 4! ways
G slots = 4! ways
Total = 4! * 4! = 24 * 24 = 576 → III is possible

Quick eliminate 72:
Only totals here are factorial products of equal-size groups (k! * k!). For k=3 → 36; k=4 → 576. No 72.

72 would need 3!*4! / 2 or some mixing, which the fixed alternation forbids.

Answer

I and III only → D
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