The Expanding Lily
brainteaser
A single water lily is growing across a quiet pond. Each day, the total surface area covered by the lily becomes exactly twice what it covered the day before. The growth continues at this steady rate, and at the end of the thirtieth day, the lily covers the entire surface of the pond.
At the end of which day did the lily cover exactly half of the pond?
Hints
Hint 1
Hint 2
Hint 3
Solution
Commit an attempt to unseal the proof. Write your answer — right or wrong, thinking it through is the point.
On which day was exactly half the pond covered?
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