Time Measurement Riddle

After quite a few days I am posting a riddle. I assure you it’s very interesting. Though it may seem a little difficult when you first read it, maintain your cool and ponder over it again.

Suppose you have ten threads and a lighter. If a thread is lighted, it will burn for exactly one hour. The threads do not burn at constant speed, in other words it can happen that the first half of the thread is burned in 15 minutes, while the remaining part will take three quarters. How can you measure exactly 45 minutes using these threads, and what is the minimum of threads you need for this?

If you need any clarification, leave your queries as comment.

Leave your asnwers below as comments.

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Vineet Patawari

Hi, I'm Vineet Patawari. I fell in love with numbers after being scared of them for quite some time. Now, I'm here to make you feel comfortable with numbers and help you get rid of Math Phobia!

11 thoughts to “Time Measurement Riddle”

  1. Ans: 2 Threads.
    Steps:
    a) Burn thread 1 at one end and at the same time burn thread 2 at both the ends.
    b) When thread 2 burns out completly it is half an hour, and thread 1 will take another half an hour to burn out.
    c) At this half an hour, burn the other end of thread 1 as well and it will take 15 mins to burn out completely.
    Total time taken: 30 mins (thread 2) + 15 mins (2nd phase of thread 1) = 45 mins

  2. Ans: 2 Threads.
    Steps:
    a) Burn thread 1 at one end and at the same time burn thread 2 at both the ends.
    b) When thread 2 burns out completly it is half an hour, and thread 1 will take another half an hour to burn out.
    c) At this half an hour, burn the other end of thread 1 as well and it will take 15 mins to burn out completely.
    Total time taken: 30 mins (thread 1) + 15 mins (2nd phase of thread 2)

  3. only 1 thread is required
    lighten one end of the thread till it burns half which takes 15 min
    and the remainning half takes 45 min so it can be measured directly

  4. i have a different solution burn 1 thread from both the ends and the 2 thread at 4 places since the whole thread takes 1hr to burn completely the time in which individual pieces burn till completion is 15min (30+15)min

  5. Firstly there are eleven threads in the picture.
    Answer to the riddle:
    Only one thread is required…
    a. burn the thread from one side
    b.After 30 min the thread would have burned half.
    c.now, burn the thread from the other end also.
    d.after 15 min. the complete thread is burned.
    so, (30+15) min.=45 min.

    1. Thanks Govind for pointing out about 11 threads in the picture. Though the pic has nothing to do with the question.

      Your answer is not completely correct. Think about it 🙂

      Keep commenting!!

      -Vineet

  6. min.’m 2 threads r required…
    1. burn both d threads( one from both d ends & d other from just 1 end)
    2.After 30 min., first thread would have burned completely and other would require another 30 min. to burn completely.
    3.after 15 min. d second one will also gt burned.

    so, (30+15) min.=45 min.

    1. min.’m 2 threads r required…
      1. burn both d threads( one from both d ends & d other from just 1 end)
      2.After 30 min., first thread would have burned completely and other would require another 30 min. to burn completely.
      3.now, burn d second thread from d other end also.
      3.after 15 min. d second one will also gt burned.
      so, (30+15) min.=45 min.

  7. 2 Threads:

    Burn Thread 1 from both ends: Time taken will be 30 Min

    The, Burn thread 2 from both ends and centre: Time taken to burn is 15 Min

    Total 45 Min

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