A problem that invites you to calculate, but the calculation is not what matters.
The boat and the ladder
Riddle statement
A boat is moored to the dock. On its side there is a ladder with 10 steps visible above the water, 20 cm apart.
The tide rises 15 cm per hour.
In 2 hours, how many steps will still be visible above the water?
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Solution
Answer: 10 steps will still be visible.
Although the tide rises 30 cm in two hours, the boat also rises with the tide. Since the ladder is attached to the boat, it rises with it.
Therefore, the distance between the water and the visible part of the ladder does not change. No additional steps are covered.