2007-05-04

How do you measure 45 minutes?

Here's one of my favorite puzzles. You have to, like, PROMISE not to go a-googling for the answer.

You have two pieces of string. They are of different lengths and different materials. All you know is that each one, when lit on the end, takes exactly one hour to burn up completely. You can't assume that either burns at a consistent rate; for instance, one may burn quickly at first and slow down near the end, and the other may (or may not) do the opposite.

Using only the strings and some matches, how do you measure 45 minutes?

[Hat tip to Darren.]

Send me your favorite ones.

3 comments:

Anonymous said...

Am I allowed to make a sundial out of the matches, using the string as a measurement tool?

I might be able to figure out longitude this way as well, but I don't know that I'd have enough matches left over to make a sextant.

Mark Hanington said...

I'm part way there... If you tie either string in a loop, and then light anywhere on the circumference of the loop, the fires will head off in two different directions around the loop. Regardless of the speeds at which they travel relative to one another, they will meet up exactly 30 minutes later. Now I just need to work out the rest...

fiona-h said...

right track...