[pdurrant]

Originally Posted by LazyScot

Spoiler:

Take two fuses. Lay them out parallel.

Light one from one end, and the other from the other end.

Extinguish when the burn points of the two "meet" somewhere along the line.

You must now have two two minute fuses.

Now lay those two in parallel.

Light one from one end and one from the other end.

Extinguish when the burn points of the two "meet" somewhere along the line.

You now must have two one minute fuse.

Now lay those two in parallel.

Light one from one end and one from the other end.

Extinguish when the burn points of the two "meet" somewhere along the line.

You now have two 30 second fuses.

Take one of the four minute fuses, and light it, and light the 30 second fuse at the same time.

When the 30 second fuse goes out, either extinguish the four minute fuse to give you a 3:30 fuse, or put your eye into the boiling water (you did remember to start the water boiling, didn't you?).

And if extinguishing is impossible, you should be able to "move" the fuses that are burning....

Correct?

This only needs 3 fuses....

No, sorry that doesn't work.

Spoiler:

The fuses burn at an uneven rate (stated in the question). This means (in extreme cases) that one might burn 1/3 of its length in 1 minute, the next 2/3 in three minutes. Another might burn 2/3 of its length in 1 minute and the next 1/3 in three minutes. Your scheme of extinguishing when the burn points meet would give you a three minute fuse (in this case) not a two minute fuse. And that's without considering that the fuses might not be the same physical length... although I admit that isn't explicitly stated in the question.

Do have another go!