Sunday, May 11, 2014

Measure 45 minutes

Problem

You have two strings of rough non-countinuous composition (in other words these strings are not ideally uniform.) You know that each will take exactly half an hour to burn no matter which end is lit. How can you measure a time interval of 45 minutes with
1.2 match sticks available
2.only one match (which only sustains a flame for a few seconds)

Solution

Solution with 2 matches...
Old solution for 2 matches.
1.Burn one string full..measure 30 min.
2. Burn second string from both sides..and measure 15 min.
3. Total time measure = 45 min.

Idea - Now we have one match..which means we can light it only once..some how we have to make sure that after the first string is burn...the second one start's with the left over fire of the first.

Solution - Make a ring of the second string and tie it up at the end of the first string.
1. First string will burn in 30 min.
2. When the first string ends, the second string is a ring so it would start off to burn at both the ends parallely and would end in 15 min.
3. Total time = 30 + 15 = 45, 1 match used.

References

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