Brain Teasers
The Troll Bridge 5
A bridge was guarded by an evil troll. The troll was very intelligent, but he was also a coward. He was afraid of anyone smarter than him. So every time anyone tried to cross the bridge, the troll would set up a test. If the traveler passed the test, he would be allowed to cross. Otherwise, the troll would eat him.
Three travelers came across the bridge. The troll told them, "You may only cross my bridge if you know the password." He wrote six three-letter words on a rock. The six words were INN, PEN, PET, PIE, TEE, and TIE.
He then said, "I will tell each of you a different letter from the password. If you know what the password is, I will let you pass. But don't tell anyone else your letter." He then whispered a letter from the password to each traveler so that neither of the other two could hear him.
A minute later, the troll asked all three travelers at the same time, "Do you know how many vowels are in the password?" "No," they all said.
A minute later, the troll asked all three travelers at the same time, "Now do you know how many vowels are in the password?" "No", they said again.
A minute later, the troll asked only one of the three travelers, "Do you know what the password is?" "Yes," said the traveler, and the troll let all three of them pass.
So, what is the password?
Three travelers came across the bridge. The troll told them, "You may only cross my bridge if you know the password." He wrote six three-letter words on a rock. The six words were INN, PEN, PET, PIE, TEE, and TIE.
He then said, "I will tell each of you a different letter from the password. If you know what the password is, I will let you pass. But don't tell anyone else your letter." He then whispered a letter from the password to each traveler so that neither of the other two could hear him.
A minute later, the troll asked all three travelers at the same time, "Do you know how many vowels are in the password?" "No," they all said.
A minute later, the troll asked all three travelers at the same time, "Now do you know how many vowels are in the password?" "No", they said again.
A minute later, the troll asked only one of the three travelers, "Do you know what the password is?" "Yes," said the traveler, and the troll let all three of them pass.
So, what is the password?
Answer
The password is PET.The six words have only five letters between them: E, I, N, P, and T. INN and PEN, both of which contain one vowel, are the only two of the six words to contain N. When all three travelers responded "no" to the troll's first answer, they knew that none of them had been told N. So the password cannot be INN or PEN.
Of the four remaining words, PIE and TIE, which both contain two vowels, are the only two containing I. When all three travelers answered "no" to the troll's second question, they knew that none of them had been told I, and that the password cannot be PIE or TIE.
This leaves only PET and TEE. Although both words contain both E and T, PET is the only one of the two words containing P. The traveler who answered "yes" to the troll's third question must have been told P.
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Comments
Ah! The troll returns. I found this one to be more straightforward than its predecessors. I was able to solve it pretty quickly in my head. Maybe I'm starting to think like a troll? Nice teaser! Thanks.
Well, this is very VERY similar to the first Troll Bridge teaser, if you really think about it.
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