You have three hourglasses. One is 5 minutes, one is 4 minutes, and one is 3 minutes. You want to boil an egg for 2 minutes. How do you do it?
Think you have it? The answer is below.
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Answer: Start the 5-minute and 3-minute glasses together. When the 3-minute glass empties, drop the egg in; when the 5-minute glass empties, take it out — exactly 2 minutes.
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📖 The answer, explained
The trick here is that you don't need a device that measures two minutes directly — you just need the *gap* between two things that finish at different times. The five and three-minute glasses start together, so they're racing toward two different finish lines. The three-minute one crosses first, and that moment becomes your new starting line. The five-minute one keeps running underneath, unaffected, until it finishes two minutes later. That leftover stretch, the space between one glass emptying and the other catching up, is exactly the window you were hunting for. The four-minute glass is pure misdirection, sitting there looking useful while doing nothing at all. It's a nice reminder that timing puzzles aren't really about the tools you're given, but about the differences between them.
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