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Table of contents
1.
Introduction
2.
Problem Statement
3.
Solution
4.
Frequently Asked Questions
4.1.
How much time can we measure by burning a rope completely?
4.2.
How much time can we measure by burning a rope from both its sides?
4.3.
How much will it take if we burn an already half-burnt rope from both sides?
4.4.
How much will it take if we burn an already half-burnt rope from only one side?
4.5.
Can we measure 45 min using two ropes?
5.
Conclusion
Last Updated: Mar 27, 2024

Measuring Time by Burning Ropes

Author Komal Shaw
0 upvote
Master Python: Predicting weather forecasts
Speaker
Ashwin Goyal
Product Manager @
Interview Puzzles

Introduction

In this article, we will go through the Measuring Time by Burning ropes Puzzle Question.

These types of questions are often asked in Interviews. So, we will be going through the problem statement and then analyzing it to get a better understanding.

Problem Statement

You have two ropes and a box of matches. Each rope takes exactly one hour to burn, but they may not necessarily burn evenly – i.e., the first half might burn in the first 10 minutes and the second in the remaining 50). What durations of time can you measure using the 2 ropes? Times do not have to start when the first rope is lit.

Note that this is a multiple-choice question. Mark all the times which are measurable.

 

Select your answer from the following options:

  • 1 hour
  • 30 minutes
  • 45 minutes
  • 15 minutes
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Solution

  1. On burning a single rope from one side, we can measure 1 hour.
  2. By burning a single rope from both sides, we can measure 30 minutes.
  3. When we burn rope 1 from both sides and at the same time burn rope 2 from only one side, then by the time the 1st rope gets completely burnt, i.e., 30 mins is over, and by this time, rope 2 would have been half burnt, then at that time, we will burn the other end of the rope 2 as well.
    Thus burning the other half of rope 2 will take 15 min. Thus finally, when the 2nd rope is wholly burnt, 45 minutes would have elapsed.

 

Therefore, we can measure 1 hour, 30 minutes, 45 minutes, 15 minutes by burning the ropes.

Frequently Asked Questions

How much time can we measure by burning a rope completely?

We can measure 1 hour.

How much time can we measure by burning a rope from both its sides?

We can measure 30 min.

How much will it take if we burn an already half-burnt rope from both sides?

It will take 15 min.

How much will it take if we burn an already half-burnt rope from only one side?

It will take 30 min.

Can we measure 45 min using two ropes?

Yes, we can measure 45 min using 2 ropes.

Conclusion

In this article, we have extensively discussed the approach for the Puzzle “Measuring Time by Burning ropes.” We hope that this blog has helped you understand the process. 

Recommended Readings:


Do check out The Interview guide for Product Based Companies as well as some of the Popular Interview Problems from Top companies like Amazon, Adobe, Google, etc. on Coding Ninjas Studio.

Also check out some of the Guided Paths on topics such as Interview Puzzles, Data Structure and Algorithms, Competitive Programming, Operating Systems, Computer Networks, etc. as well as some Contests, Test Series, Interview Bundles, and some Interview Experiences curated by top Industry Experts only on Coding Ninjas Studio.

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