MCN Professionals | Interview Question of the day
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Date: 9th Sept;
2011
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Difficulty Level: ***
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Category: Puzzle
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Today's Question:
You have two identical ropes, which are non-uniform in
composition. Each rope takes 60 minutes to burn (But non-uniformly, for
example: 90% of the rope may burn in 5 min and rest 10% may take 55 min or any
such composition). You don't have any watch but a lighter. How will you
calculate 45 minutes?
Solution:
The
ropes are non-uniform, it means that if we cut a rope in two halves, then both
halves may not take 30 minutes each to burn (But on a whole the rope
will take 60 minutes to burn).
To calculate 30
minutes, you only need 1 rope
- Lit the rope from both ends, it
will take the rope 30 minutes to burn completely
To calculate 45
minutes, you need 2 ropes, Lets call the ropes A &
B. Follow the below process:
- Burn Rope-A from both ends and
Rope-B from one end.
- Rope-A will completely burn in 30
minutes (because it is put on fire from both ends). when Rope-A is burnt
completely, Rope-B would have burnt for 30 minutes (It does not
mean that Rope-B is half burnt), At this point lit the other end of Rope-B
as well, it will take another 15 minutes for Rope-B to burn completely.
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