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## The Stealing Mailman 5

This is a fairly simple problem that can cause some people trouble. Kevin and Sophia want to mail high confidential letters between each other. They know that the mailman is crooked and opens the letters. Each of them has their own key and matching lock, and Sophia has a wooden box she plans on locking.

Neither key can be used on the other lock. Using the box, how can the two successfully mail letters between each other without the mailman seeing?

see explanation

1) Sophia sends the locked box with her letter to Kevin. 2) Kevin adds his lock to the box and mails it back to Sophia. 3) Sophia gets the box, removes her lock and mails it to Kevin. 4) Voila! Kevin can now open the box using his key.

David Walker

The given solution is rather roundabout, especially if Kevin and Sophia are going to be exchanging a lot of letters. Here's a more efficient one: 1. Kevin mails Sophie his lock (in an open position). 2. Sophie puts her letter in the box, along with her own lock (open), locks the box with Kevin's lock, and mails it. 3. When Kevin receives the box, he opens it with his key. After reading Sophie's letter, he puts his own letter in the box, along with his (open) lock, and locks it with Sophie's lock. And so on.

Paulo

nice!

brainfry

How did Kevin open the lock in step 2?

Tarun245

No, fried brain, he put on his own lock.

Joe Weinberger

Kevin never would have been able to open Sophia's lock from step 1 to put his lock on in step 2....this puzzle is retarded.

David Walker

He didn't have to unlock it to put his own lock on.

Caleb Briggs

Since the puzzle is not specific, it is possible to do this in 1 step. Kevin can lock and mail the box which as the letters, and then mail his key and the box sperately, because it doesn't say the mailman takes anything in the letters. Then Sophia can open the box, take the letters, then lock and send the box and the keys back separately again.

Caleb Briggs

Since the puzzle is not specific, it is possible to do this in 1 step. Kevin can lock and mail the box which as the letters, and then mail his key and the box sperately, because it doesn't say the mailman takes anything in the letters. Then Sophia can open the box, take the letters, then lock and send the box and the keys back separately again.

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Submitted by
Ravi