Brain Quiz #15

Ian and Sydney are staying in different rooms in the same hotel. Ian needs to give a gold pendant to Sydney, but both are unable to leave their room. The only way they can transfer objects is by using the bellhops. Both Ian and Sydney have a safe with a large clasp that can be secured with padlocks. Both Ian and Sydney have a padlock and a corresponding key. (So 1 gold pendant, 2 safes, 2 padlocks, and 2 keys.) But the bellhops are thieves. Anything that is not padlocked in the safe will be stolen by the bellhops – including any unlocked padlocks, the keys or the pendant. How can Ian transfer the gold pendant to Sydney without it being stolen?

Difficulty Rating: 14

14 thoughts on “Brain Quiz #15

  1. Just to be clear: The padlocks and keys are distinct:
    E.g. Ian has a blue key that goes with his blue padlock.
    Sydney has a red key that goes with her red padlock.

  2. sydney sends her padlocked safe to ian
    ian locks his padlock onto her safe and sends it back
    sydney removes her padlock and sends back the safe
    ian unlocks it, puts in the pendant, and locks it again and sends it back
    sydney locks it with her lock, sends it back, ian removes his lock, sends it back and sydney opens the safe with the pendant.

    this all assumes there can be two locks on the safe at the same time….

  3. 1. Ian puts the pendant in his safe.
    2. Ian locks the safe with his padlock.
    3. Ian sends the safe to Syndney.
    4. Sydney locks the safe he received from Ian with his padlock as well. (Ian’s safe now has the pendant inside and two padlocks on it.)
    5. Sydney sends the safe back to Ian.
    6. Ian unlocks his padlock and takes it off the safe.
    7. Ian sends the safe back to Sydney.
    8. Sydney retrieves the pendat by unlocking his padlock on the safe.

  4. Just a scoring note. Paul and Luke were both right, and answered at almost the same time. Paul was first, but I gave them both the bonus points, because Luke’s answer was better/more efficient.

  5. Ian puts the pendant in his safe, locked with his lock. He sends it to Sydney who adds her lock to the safe (now secured with both locks) and sends it back. Ian takes off his lock and returns the safe to Sydney who opens her own lock and retrieves the pendant.

  6. assuming that the safe can handle two locks…

    Ian places the pendant in the safe, locks it and sends it to Sydney. Sydney places her lock on, and sends it back. Ian takes his off and sends it back to Sydney. She takes her lock off and TADA! the pendant is revealed.

  7. This would depend on the shapes of the clasp and padlocks, so it might not be what you’re looking for, but here goes:

    Sydney locks her padlock onto either the door or the body of her safe, but not both, so it’s locked on but the safe is still open. She sends the safe to Ian. Ian puts the pendant in the safe, then locks the other part (door if Sydney chose frame, and vice versa) onto Sydney’s lock in such a way that the door of the safe is locked closed. He sends it back. Sydney unlocks her lock (leaving Ian’s lock still attached to the safe) and gets the pendant.

  8. Ian puts the pendant in the safe.
    Ian padlocks the safe.
    Ian sends the safe to Sydney.
    Sydney padlocks the safe with her padlock.
    Sydney sends the safe back to Ian.
    Ian removes his padlock.
    Ian sends the safe back to Sydney.
    Sydney removes her padlock and gets the pendant.

    I just KNEW studying public-key cryptography would come in handy one of these days…

  9. Ok, looks like I was wrong. Here’s one that makes more sense:

    Ian locks the pendant in the safe and sends it over. Sydney puts her lock on the safe too, so it’s locked twice, and sends it back. Ian removes his lock, but the safe is still locked by Sydney’s lock. Back to Sydney it goes, and she takes off her lock and has the pendant.

    This is the kind of brain quiz I like–seems impossible until you get it, and then it seems obvious. Funny how I understood early on that saying “can be secured with padlocks” rather than “a padlock” was a hint, but I still couldn’t get it.

  10. Ian puts the pendant in the safe and puts the padlock on and locks it. He then has a bellhop take the safe to Sydney. She now has the pendant. Since they eventually have to leave the hotel they are in, Ian slips the key to Sydney as they both exit the hotel. Thus, Sydney is able to get the pendant out of the safe with nothing being stolen.

  11. Sorry, the previous message was from, me, it’s pretty late, so my minds fuzzy, but I had 2 excedrine and I can’t sleep, so you feel the full fury of my boredom here.

    My Ron Haiku…

    Serious ever?
    Can’t eat more Max and Ermas.
    Wit dry as saw dust

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