Wednesday, February 16, 2011

Two Threads Are Bruning.?????

You have two lengths of rope. Each rope has the property that if you light it on fire at one end, it will take exactly 60 minutes to burn to the other end. Note that the ropes will not burn at a consistent speed the entire time (for example, it's possible that the first 90% of a rope will burn in 1 minute, and the last 10% will take the additional 59 minutes to burn).

Given these two ropes and a matchbook, can you find a way to measure out exactly 45 minutes?

1 comment:

sriram said...

You have two ropes.

one rope will take 60 minuites to burn completely.

light the first rope from two ends .
light the second rope from only one end.

after 30 minuites , the first rope will burn completely and second rope will burn half(so it can still burn for another 30 minuites).

Now light the second rope on the second end. In 15 minuites , the second rope will completely burn.

so the total time is 30+15 = 45 minuites.

-Sriram Thallam