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Think Like a Mathematician: Problem-Solving Strategies

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Section 1 of 425%

The Locker Puzzle

The Locker Puzzle

Imagine a school corridor with 10 lockers, all shut. Student 1 opens every locker. Student 2 closes every 2nd locker. Student 3 changes every 3rd locker (opens it if shut, closes it if open). This continues up to Student 10. Which lockers are open at the end? Don't try to solve it yet — just think: where would you even start? This kind of puzzle feels impossible until you pick the right strategy. That is exactly what today's lesson is about.

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