Solution to the 15 Minute Problem
Follow the following steps to measure 15 minutes:
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Reverse both the 7 and the 11 minute hourglasses
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Let the time pass for 7 minutes
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Reverse the 7 minute hourglass
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Let the time pass for 4 minutes
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Reverse the 7 minute hourglass
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Let the time pass for 4 minutes
Solution to the 24 Minute Problem
Follow the following steps to measure 24 minutes:
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Reverse both the 7 and the 11 minute hourglasses
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Let the time pass for 7 minutes
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Reverse the 7 minute hourglass
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Let the time pass for 4 minutes
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Reverse the 11 minute hourglass
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Let the time pass for 3 minutes
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Reverse the 11 minute hourglass
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Let the time pass for 3 minutes
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Reverse the 7 minute hourglass
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Let the time pass for 7 minutes