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Waiting for green
A bag holds red, green and blue balls. You draw balls one at a time without looking and without putting any back. What is the fewest number of draws that guarantees at least green balls?
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Hint
The worst case takes every ball that is not green first.
Solution
- In the worst case all red and blue balls come out first.
- After that every draw is green, so more draws give green balls.
- With fewer than draws the worst case still leaves you short, so the answer is .
Answer: