## Monday, February 9, 2009

### Two sticks.

You have two sticks each of which can be lit and burn homogeneously for an hour. How can you measure 45 mins with these sticks, without using any additional measuring device? (this is a very old puzzles)

rachel said...

So, here are two answers. The first is my solution, the second is my 12 year old son's solution.

Solution #1: light both sticks at the same time, but light one of them from both ends. When the stick that was lit from both ends has burned up, 30 minutes have elapsed, and the other stick is only half consumed. At that time, light the second end of the remaining stick and it will burn up in another 15 mintues, giving you a total burn time of 45 minutes.

Solution #2: Line up the sticks next to each other, and light each one at opposite ends. When the flames reach each other, 30 minutes have elapsed. At that time, put out the flames, and line the shorter sticks up next to each other, and again light from opposite ends. When the flames reach each other, another 15 minutes have elapsed, again giving a total burn time of 45 minutes.

Maria said...

Wow! I did not know the second solution even existed. You are both getting a prize. Bravo!!!