You have two watches: - clock A is completely stopped;
- Clock B works, but it goes back exactly 1 minute every hour. Which of the two keeps the correct time more times?
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The two broken clocks
One seems useless and the other, at least, moves. The trick of this puzzle is separating appearance from the actual frequency with which each clock is right.
Hints
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- Don't ask which one seems more messed up, but which one gets it right more often.
- A stopped clock has a periodicity of success that is very easy to count.
Solution
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Answer: The clock stopped. Explanation: A stopped clock shows the correct time twice a day. On the other hand, a clock that loses one minute per hour only returns to the real time when it has accumulated 12 hours of delay. Since you lose 1 minute per hour, that happens every 720 hours, that is, every 30 days. So, although it may seem worse, the stopped clock is right much more often.
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