Ali Baba and the Forty Thieves
Ali Baba wrote the number `17` on a piece of paper. The forty thieves pass the paper to each other, and each one either adds `1` to the existing number, or subtracts `1`, until each of them has done so once, and then they return the paper to Ali Baba.
Is it possible that the number now written on the paper is `40`?
Difficulty level (1 very easy - 10 very hard): 3
Topics:
Arithmetic
Combinatorics
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Invariants
Logic
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Reasoning / Logic
Number Theory
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Division
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Parity (Even/Odd)
Combinatorics
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Case Analysis / Checking Cases
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Processes / Procedures
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