You have two candles. Each candle takes 60 minutes to burn completely. There's one complication: the candles are not uniform and cannot be assumed to burn evenly. Using these two candles and nothing else, how would you time exactly 45 minutes?
Please email your solution to John Kador ([email protected]) using the subject line “Candle Time.” Deadline is June 25, 2009. Two accurate responses will be selected to receive a signed copy of John Kador's How to Ace the Brainteaser Job Interview. Creativity and elegance increase one's odds. Good luck.
BRAINTEASER: WORDS IN COMMON
All of these words share the same property. What do they have in common?
Solution at bottom.
SOLUTION TO PREVIOUS PUZZLER: PADLOCK PROBLEM
To recap: Andy needs to send his associate Bob a highly sensitive document for Bob's eyes only. Andy and Bob have a number of padlocks with corresponding keys and a portable safe. Bob does not have keys to any of Andy's padlocks. The messenger will faithfully deliver the safe but cannot be trusted to respect the confidentiality of the safe's contents; if he can open the box in transit, he will. How can Andy securely send the document so that Bob and only Bob will see it?
Solution: The keys are never entrusted to the messenger. Andy sends Bob an empty safe with nothing inside but an open padlock. When Bob gets the safe, he puts one of his own open padlocks into the safe, and locks it with Andy's padlock. Bob sends the safe back to Andy. Now Andy opens the safe by unlocking his own padlock with his own key, puts the document into the safe, and secures it with Bob's padlock, and sends the safe back to Bob. Bob then opens the safe with the key to his own padlock. [Ed. Note: We apologize to our readers, as the original puzzle said that only Andy had padlocks and keys, whereas the solution requires that both Andy and Bob have their own padlock and corresponding key.]
We received many entries but, given the untrustworthiness of the courier, none of the suggested solutions would have guaranteed the confidentiality of the documents. For example, one reader from New York suggested the following solution:
Andy should have the messenger deliver just a key to Bob. Then, in a separate delivery, have the messenger deliver the safe (with the document locked inside), secured with the padlock which can be opened with the key in Bob's possession.
The trouble with this solution is that there is no way to prevent the messenger from copying the key.
John Kador is the author of 10 books. His latest book is Effective Apology: Mending Fences, Building Bridges, and Restoring Trust (Berrett-Koehler). www.effectiveapology.com
SOLUTION TO WORDS IN COMMON: All the words are palindromic in that the letter occupying the first position of each word can be moved to the last position and the word, read backward,is the same as the original.