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Ubi-Ubi's Ruby

  1. Oct 23, 2006 #1
    My friend gave me a brainteaser and i wasnt able to solve so i was hoping you guys could help me out with this. Thnx in advance. So here it is:

    Ubi-Ubi's Ruby

    During the sixteeth century, an English explorer was sailing in uncharted waters trying to find a faster route to India. Caught in a sudden squall, his vessel was blown to shore and grounded on a sandbar. He and the crew rowed to shore in search of help, and soon discovered a village of friendly people. Unfortunately, they had discovered the Ubi-Ubi, whose crops are always plentiful and whose life is leisurely- and sometimes very boring. The Ubi-Ubi will go to great lengths to enterain themselves, sometimes at the expense of others. The chief agreed to help the explorer get his ship off the sandbar on the condition that the explorer solve a riddle for the amusement of the whole tribe. He then signaled to three men, who came forward carrying covered baskets. While the entire tribe giggled, the explorer was told that the three men were Qubi, Lubi, and Subi (in some order), and that two of the baskets contained cobras and the third an immense ruby. The chief explained that the explorer's job was to determine the men's correct names, and pick the basket containing the ruby. If he was correct, he could keep the ruby and the entire tribe would get the ship off the sandbar- but if we chose wrongly, the cobra would bite him, and the crew would have to remain and amuse the tribe. Each man would make three statements* to help the explorer determine the truth; however, as one final clue, the chief told the explorer that one man always lied, on always told the truth, and the third always lied on odd days and told the truth on even days.
    Unfortunately, the explorer was not very good at logic, and after pondering the three men's statements, chose the wrong basket. He opened the basket to reveal an immense cream pie, which the chief immediately threw into the explorer's face laughing uproariously. The entire tribe then turned out and cheerfully pushed the ship off the sandbar, and waved happily as the explorer and his men sailed off to more adventures.
    Can you do better than the explorer and correctly detemine the three men's names, the date, and the basket containing the ruby?

    *The 3 statement made by the 3 men:

    Native #1:

    Today is the 23rd of the month
    #2 is a liar
    The ruby is not in my basket

    Native #2:

    I am Subi
    Today is an even day
    Native #3 is Lubi

    Native #3:

    I am Subi
    Lubi has the ruby
    Today is the 22nd.

    Thanks for the help guys!
  2. jcsd
  3. Oct 23, 2006 #2


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    Only the always-lying native will lie, and the other two will tell the truth. Clearly, 1 is lying because he's saying it's the 23rd, which is odd, so 2 and 3 must be telling the truth. But both 2 and 3 say their names are Subi, so they can't both be telling the truth. This is a contradiction.


    On an odd day, the always-truth-telling one will tell the truth, the other two will lie. Clearly, 2 and 3 are lying 2 says it's an even day, and 3 says it's the 22nd, which is an even day. So NATIVE 1 IS THE TRUTH-TELLING ONE, and he says it's the 23rd, so THE DATE IS THE 23RD. Both 2 and 3 are lying, and both call themselves Subi, so neither of them are Subi, so NATIVE 1 IS SUBI. 2 is lying but says Native 3 is Lubi, so native 3 must in fact not be Lubi so NATIVE 2 IS LUBI, NATIVE 3 IS QUBI. Native 1 is telling the truth, and he says 2 is a liar, so NATIVE 2 IS THE LIAR, and NATIVE 3 IS THE ONE THAT CHANGES DAY-TO-DAY. Native 1 says he doesn't have the ruby, so he really doesn't (i.e. Subi doesn't). Native 3 says Lubi has it, but 3 is a liar, so Lubi doesn't. This means QUBI HAS THE RUBY.


    Native 1: Subi, always truthful, doesn't have the ruby
    Native 2: Lubi, always lies, doesn't have the ruby
    Native 3: Qubi, changes day-to-day, does have the ruby
    Date: 23rd of the month
  4. Oct 23, 2006 #3
    omg thank you!! I never though of it like that. Thnak you again
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