that was cool
so first one when we burn it from 2 sides so it takes 30 mintues to finsih,,,and so we stop the second one at one length that measures 3o mins and then we burn the 2nd one from either side so it takes 15 min ,,cool answer nice

It should be placed in the "Very easy" category but it was a nice puzzle i guess.

@3: It's a figure of speech. It means not to overexert yourself.

Pfft - the problem states what will happen if we light one end of the string. Nothing is said about the behavior of the string when we light both ends. This solution assumes conditions not stated in the problem.

Weak.

To McWyrm: The problem tells you THE PROPERY of a string when lighting an end. If u light it at any of the ends, no matter how it burns it will burn fully in 1 hour, if u light it at both ends - no matter where the fire is or how fast it burns, it will burn twice as fast! The problem is very easy and quite logical.

what?
it seem like it goes like this:

1) light one string both ends = 30 mins
2) light next string = 1 hr

total of 1 hour 30 minutes

Why can't you fold one string in half twice and then light it at either of the folds that's not in the middle?

I just thought would it be possible to cut the other string to half and light it from all ends same time lighting both ends of the other string :D

As the property of the string is not uniform, cuting the string will not help!!!

Nice puzzle!

this was pretty interesting though, but rather simple. think for a while, and you got the answer! :)

but i like it!!!

Steps of answers previously explained:

1) The first string is lit from both ends, and the second string is lit from one end (simultaneously).

2) When the first string is burned completely, it would have taken 30 minutes. At this time you light the second string's other end. Assuming that the remaining time to burn the second string was 30 minutes if left to continue burning from only one end, this would now take 15 minutes (once both sides are lighted).

However*

Quote: "The rate at which the strings will burn is completely random and each string is different."

If this statement is true, then that would mean when the first string had finished burning, the second string would not necessarily have 30 minutes of time remaining.