Sunday, February 15, 2015

Riddle/Lateral Thinking: The Burning Thread

4. The Burning Thread


There are 2 threads of different lengths. Each takes one hour to burn. You've a lighter to ignite. 

Q: how to measure exactly 45 minutes


Note: Basic assumption holds good. 

Read it and post your answers as reply to the post. I will be adding my answer if there are no correct answers after 10 replies.  

Regards

1 comment:

Karthik Devisetty said...

Light the 1st thread on both the sides so that it burns out in half an hour. Light the 2nd thread on one side at the same time you light the two sides of the 1st thread. This means that in 30 minutes the 1st thread would be completely burnt out and half of the second one would be left. After the 1st thread is completely burnt out i.e., 30 minutes, light the second side of the 2nd thread so that the remaining half of the 2nd thread which usually takes 30 minutes to burn if lit on one side now burns out totally in 15 minutes. So you can calculate the total time taken (30+15 min)