Two ropes, 45 minutes
You have two ropes and a lighter. Each rope takes exactly 60 minutes to burn from one end to the other, but neither burns at a uniform rate — half a rope might burn in 5 minutes and the rest in 55. Using only the ropes and the lighter, how do you measure exactly 45 minutes?
Show hints (2)+
- Burning a rope from both ends halves its total time.
- You can light a second end partway through.
Answer
This is an open-ended question — work through it and compare your reasoning.
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Asked at: Jane Street, Optiver