You have a lighter and two ropes that take exactly one hour to burn, but they don’t burn at a steady rate. For example, one rope could take 59 minutes to burn the first inch and then burn the rest of the rope in the last minute.
How would you use these two ropes to measure 45 minutes?
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Light the first rope on both ends and the second rope at only one end. When the first rope burns out you know 30 minutes have passed. Light the other end of the second rope and when it burns out, 45 minutes have passed.
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A boat has a ladder that has six rungs. Each rung is one foot apart. The bottom rung is one foot from the water. The tide rises at 12 inches every 15 minutes. High tide peaks in one hour.
When the tide is at its highest, how many rungs are under water?
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None. The boat is floating on the water, so as the tide rises, so does the ladder.
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