Measuring 45 seconds with two irregular fuses
Question
You have two fuses, each of which takes exactly one minute to burn end to end, but they burn unevenly so length tells you nothing about time. How can you time exactly seconds?
Short answer
Light fuse A at both ends and fuse B at one end together. A burns out after seconds; at that moment light B's other end. B's remaining seconds of burn now goes twice as fast and ends seconds later, at seconds.
Adapted from Crack, Heard on the Street, Q1.52, p.19; question and answer rewritten by SelfMadeQuant.com.
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Open the worked solutionLessons behind this question
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
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