Two uneven ropes
There are two ropes which are of different length.
Each rope takes 60 minutes to burn completely when set on fire from one end.
You have to measure 45 minutes of time with the help of this ropes.
You cannot fold the ropes to half or tamper any of them.
The considering point over here is that neither of the ropes can be folded.
Take any of the rope , and set it on fire from both the ends. (Lets consider this as rope A)
At the same time, light up the other rope (rope B) from one end.
Now when the first rope (rope A) gets completely burnt, light up the second rope from the other end.
When the second rope completely burns, the entire process from the beginning would have taken 45 minutes.
It would take exactly 30 minutes for the rope A to completely burn when set on fire from both the ends.
At the same time rope B is also set on fire from on end.
So, when rope completely burns, rope B would’ve exactly burnt through it’s half way.
Rope B would still require 30 more minutes to burn completely.
By now we have measured 30 minutes, and now we need 15 more minutes.
So now, light up the other end of rope B.
Rope B would burn completely by 15 minutes.
Thus, 30 + 15 = 45
Take the two ropes and tie them together around halfway of each other. Then take both of the ends of ropes and tie those together around halfway as well. After setting aflame the bottom ends of the rope, just wait until they reach the second knot. 45 Minutes will have passed.
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