Measuring time using Ropes
You have two ropes.
Each of them burns for one hour. They burn unevenly in different parts though – it means that one half can burn for 20 minutes and other half for 40 minutes. In addition you have a box of matches.
Measure 15 minutes!
When you light a rope from both ends it burns in half an hour.
You only need to light both ends of one rope and one end of the other. When the first burns out you light the second end of second rope. Half hour is burned away from that one already. The rest burns out in 15 minutes, burning from both ends.
the first half burns in 20min. and other half in 40 min. ,
consider this as the rope,( ‘ = ‘ is the rope part , ‘ D ‘ is an end point ‘ H ‘ is a joint)
0================================0
now bring the two ends together,
================D
H
================D
now again bring the ends at left and right together,
========D
| ========D
H H
| ========H
========H–^
now light one of the D ends and wait for the flame to burn the first H . fifteen minutes are over by then.
Step1: Ignite both the ends of the first rope and only 1 end of the second rope. at the same time As soon as your first rope is burnt completely in 30 mins, you are left with 30 min of the other rope with one end unburnt.
Step2: Now ignite both the ends of the leftover 30 min length of rope 2, it will burn in 15 mins.
Your Answer
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