You have two ropes. You know that each rope takes one hour to burn from one end to the other, but that the burning does not take place at a constant rate (i.e. half the rope may burn in one minute, and the other half will take 59 more minutes to burn).
How would you go about measuring a 45 minute time interval with just these two ropes?
This is the first puzzle on perplexus. You light both ends of one rope and one end of the other rope. When the first rope burns out, 30 minutes have passed. The other rope will have 30 minutes left. Then, you light the other end of that rope. It will burn out in 15 minutes. The time will be 45 minutes.

Posted by Math Man
on 20120511 21:03:09 