Possible Duplicate:
Proof of recursive formula for “fusible numbers”
There are N ropes given and
it is given that each ropes burn in 1 hour
You have to calculate 40 minutes using these. How can I do that?? I made 45 minutes, but 40 is not made by me. Help me please.
Thanks in advance.
Assuming that the ropes burn at a uniform rate, just loop one rope into three coils of equal length, thereby dividing it into thirds, and mark the end of one loop. Light the end further from the mark; your $40$ minutes will be up when the rope burns down to the mark. If no other way to mark is available, tie one of the other ropes around your burning rope at the desired point.