BrainDen.com - Brain Teasers

# Igniter Cords

## 29 posts in this topic

fold the cord into 4 equal parts and wait till 3 of three of the four parts burn

##### Share on other sites
fold the cord into 4 equal parts and wait till 3 of three of the four parts burn

That won't work. The riddle states, "different parts can burn at different speed".

##### Share on other sites
I believe this solution is also possible .. Please comment ...

1. Ignite the first cord at the two ends and somewhere approximately in the middle so that the fire from the middle propagates towards the two ends. It should take 15 minutes for this first cord to burn out completely (There would be two pieces of the first igniter cord since it was ignited at the middle as well - EVERY LAST BIT should burn out)

2. Ignite at the second cord at the two ends as soon as the first cord "completely" burns out. This would take another 30 minutes.

The only problem is that it would be almost impossible for you to find the middle point from which the cord is to burn equally in both directions. It might reach one end 5 minutes before it reaches the other (due to the uneven burning speed of the materials). Thus you would not be able to accurately measure 15 minutes.

##### Share on other sites

For those struggling with the solution, think of it with some more data, this is not part of the puzzle nor does it need to be, but will help you wrap your head around this:

Lets say each cord is 10 units long and for whatever reason the burn times for each unit are 1,2,3,4,5,6,7,8,9,15 = 60 (in Minuets), folding is half will not get you 30 sec on each side. If you light both sides they meet 1/4 the way through the 8th unit. If you have two of the cords and you light three ends the one with both burning will be gone in 30 mins the other, depending on what end you light will have 7 1/4 units left or 2 3/4 units, either way they will = 30 mins. If you light the remaining end it will take 15 mins to burn out so the total burn time is 45 mins.

Not sure why any one would manufacture detonation cord like this :-). It there a real life application to this puzzle?

My two cents!

(Really just two coins not sure if they are both worth a cent but for whatever reason I know they = 0.02 of a dollar)

• 1