This one's adapted from
http://www.rinkworks.com/brainfood/p/discrete5.shtml
You like your boiled eggs to be boiled for exactly three-and-a-half minutes.
Unfortunately, you've broken your three-and-a-half minute egg timer, and the only other timing mechanism in the house are some slow-burning four minute fuses*. NB. I mean fuses that burn for exactly four minutes, not four fuses that burn for a minute each!
Unfortunately (again), you know that the fuses do not burn at a uniform rate, so you can't just cut one of them to a three-and-half minute length.
Can you time exactly three-and-a-half minutes for your egg using the four minute fuses? If so, how?
Oh - and spoiler tags around answers please. Many thanks to all of you who remembered without me reminding you.
*No, I don't know why you have four-minute fuses in the house either. And yes, you do have some matches as well.