Half Time at Hard Time

You remember that larcenous prisoner pal Shifty. Turns out his brother-in-law Shaky, the crime ring’s explosives expert, was in the penitentiary and looking for a way out. He discovered the prison updated their security system at midnight.

At zero-hundred hours, the computer initiated the cycling process. Exactly 45 seconds later, it shut the electrified fence and alarms for mere moments, whereupon it was fully reactivated with fresh recording media. If Shaky could breach the fence at the 45-second mark, he could escape. Three seconds early or late, and his goose was cooked. And by goose, we mean an electric Shaky.

There was just one problem. A bell always clanged at midnight, but how could Shaky time 45 seconds without a watch or cell phone, both banned by incarceration rules.

Having studied under explosives master Dixon Hill, Shaky felt confident he could figure a way. He discreetly assembled fuses in the prison workshop. Although each length burned exactly one minute, they burned unevenly. The first half of this homemade det cord might burn in forty seconds while the second half races to the finish in twenty. He couldn’t depend that three quarters of a fuse would give him 45 seconds and certainly not risk his life.

But then Shaky saw the answer. Armed with two one-minute lengths of det cord and a lighter, he affected his escape. How did he do it?

Rules

1. The prison’s system reset begins at midnight when a tone sounds. Exactly 45 seconds later, the fence deactivates and mere moments later it re-electrifies.
2. Shaky carries only a lighter and two lengths of fuse cord.
3. Each cord will burn exactly one minute. However, burn rate is not even or proportional.

Here is an entertaining three minute Ted Talk presentation and answer to the puzzle.

 

 

 

 

© SleuthSayers

 

Solution

If you can’t watch the video, here’s the answer:

Burning the Incendiary at Both Ends

The title of today’s article offers a hint at the solution. Here is how Shaky can defeat the system.

1. Fold the first fuse cord in half and light both ends at once. No matter how crude the burn rate, it will take 30 seconds. Shaky still has 15 seconds to account for.
2. At the same time Shaky lights both ends of cord 1, he simultaneouosly lights one end of cord 2.
3. The second fuse still has 30 seconds to go. At the precise moment cord 1 burns out, Shaky lights the other end of cord 2.
4. As the flames of cord 2 meet and sizzle out, Shaky dives through the fence.

Unfortunately he was arrested twenty minutes later when the warden’s daughter picked up a hitchhiker.