Scientific American presents The Math Dude by Quick & Dirty TipsScientific American and Quick & Dirty Tips are both Macmillan companies.

A math puzzle a day keeps your brain saying "Yay!"

I know that’s not the most memorable saying in the world, but it’s definitely true—puzzles are a fantastic workout for your brain. As such, you’d be wise to try your hand at tackling at least a few different kinds of puzzles every week. And the best part of this is that mental exercise like this is fun!

To help you in your endeavor to start puzzling more, today we’re going to take a look at a great brain teaser that I recently ran across. This puzzle is all about time and how you can measure intervals of time in a rather unusual way: by burning bits of specially crafted string. How does it work? And what’s the big brain teaser?

That’s exactly what we’ll be talking about today.

How Can You Measure 45 Minutes?
Imagine you’ve been given several pieces of string with varying lengths and thicknesses. Not only do the lengths and widths of the pieces vary, each piece of string isn't even uniform in width along its own length. In other words, they get thicker and thinner (by different amounts and in different places) as you go from one end to the other. While all of the pieces are therefore different, they have one thing in common: if you light one end on fire, it will always take exactly 1 hour to burn through to the other side. But since each piece gets thicker and thinner as it goes, a given piece of string doesn’t necessarily burn at an even rate. By which I mean that a string doesn't necessarily burn half its length in 30 minutes—all we can say is that it burns its entire length in exactly 1 hour.