A classic puzzle conundrum goes like this: You’re in a room with two ropes and a box of matches. Each rope takes exactly an hour to burn all the way across, but it might burn faster through some sections and slower through others. Find a way to measure exactly 15 minutes.
Some sections of rope may burn faster than others, so although a full rope takes one hour to burn, you can’t assume that a quarter of the rope will take 15 minutes. If, however, you light one rope simultaneously at both ends, the rope will be fully burned after 30 minutes. (Consider the moment when the flames at each end meet. Each end will have burned for the same amount of time, and the total time must add up to one hour.) If you light one end of rope A at the same time as you light both ends of rope B, after rope B burns out A will have burned for 30 minutes—and so you know the remainder of rope A will also take 30 minutes to burn. Therefore, if you light the other end of rope A as soon as rope B’s flame burns out, it will take 15 minutes for the two burning ends of rope A to meet.
We’d love to hear from you! E-mail us at games@sciam.com to share your experience.