**IQ PUZZLE - 31 August**

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

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light one end of first string and both ends of second string at the same time. When the second string is completely burnt we have 30 min. Now light the other end of first string to get another 15 min.

ReplyDeleteLighting the string from either end or both ends can give 1hour or 30 min respectively for a string irrespective of the burning rate.

doom rocking ans

ReplyDeleteThere can be better solution, presuming that the strings burn at uniform rate. Cut one of the string into half. Now cut one of the piece into half again (i.e. one-fourth of full string). Now, light the half piece of the string. When it finish burning (it is half hour now), light one of the one-fourth piece. When this piece finishes, it should be 45 minutes.

ReplyDeleteThis way only one string will be used (and we will have a piece left to measure 15 minutes, or, if required, 7.5 minutes, etc...)

If that's the only known property of the strings, then there's no solution.

ReplyDeleteIf you light both ends of one string it might burn out completely in only 1 minute. How come? Well, suppose the string has ends A and B, and an internal point P such that burning from:

A to P takes 1 minute,

P to B takes 59 minutes,

B to P takes 1 minute,

P to A takes 59 minutes.

This rope has the property that if you light either end it will take 1 hour to burn. But if you light both ends simultaneously it burns out in only 1 minute!

You need some additional property in order to guarantee a solution.

if burning from B to P takes only 1 minute, then how come it will take 59 minutes to burn from p to B???

Deletedistance is irrelevant. it takes 1 hour to burn, two flames on each side burning for 30 minutes duration will guarantee the string is burned. since 1 hour = burned completely.

Delete"if burning from B to P takes only 1 minute, then how come it will take 59 minutes to burn from p to B???"

DeleteHow should I know? Supposedly, the only known property is that when you light one end of either string it takes exactly one hour to burn.