2007-05-30

Locked boxes

Here is a very good puzzle that I'd never heard before I came across it today. (I found it here—but don't peek yet!)

There are two locked boxes. Each box contains the other's one and only key. Each box can only be opened with its own key. How can I open both boxes?

11 comments:

Mark Hanington said...

Well, if one box were inside the other box, and you were inside both boxes, along with both keys, you could let yourself out of first the inner box and then the outer. Thatis, assuming you could use the keys from the inside as well as from the outside of each box.

fiona-h said...

VERY good!!! Also possible if you're just inside the outer box.

Mark Hanington said...

Clever puzzle. Recursive thinking...

Molly said...

Hey, you didn't say these were huge boxes, or that they could be unlocked from the inside! good one.

Zootenany Hoodlum said...

I was thinking you could just drop them from a great height.

fiona-h said...

thanks for putting a radiohead song in my head, zoot! what a great way to start the day :-)

Darren said...

I cry foul. What kind of box allows you to unlock it from the inside? (with the key or otherwise).

fiona-h said...

Here's a summary of the steps:
The boxes are different sizes.

The small box is inside the big box.

You’re inside the big box too.

The key to the small box is on the floor of the big box.

You pick it up and unlock the small box to remove the key to the big box.

You unlock the big box (its keyhole is on the inside).

fiona-h said...

And why not, Darren? Why not, I ask you?

HOWEVER, since you're feeling cheated, I should tell you that J has come up with TWO ENTIRELY DIFFERENT solutions that do not resemble the solution I had in mind at all. He's disinclined to post them, but they are very very good and don't require an inside lock.

Mr. Kite said...

Okay, I think I've let everyone have enough time to post their ideas. Here's two other solutions I came up with:

1. Assume that the keys are not physical, metal keys, but numerical keys, like the numbers that would open a combination lock. If these keys were written on scraps of paper and placed in transparent boxes, you could look inside the boxes to get the combinations to open the boxes.

2. Assume that the keys are those key cards that you swipe in front of "proximity detectors" to unlock secured doors. If each box contained the key card to the other's "proximity detector" lock, you would simply place the two boxes close to each other and the boxes would unlock.

fiona-h said...

love these!