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Home » Math and Logic Problem Exchange » Original Logic Problems Dec.2012 #72 "Ferry Tales"

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1/27/2013 2:34:29 PM

john_d_corr
john_d_corr
Posts: 3
Hello, everyone.

There seems to be a logical contradiction in this puzzle that the answer sheet doesn't take into account.

The introduction says that 5 trainees were "required to pilot a ferry from Staten Island to Battery Park", and that "Each recruit was given the chance to pilot the ferry from Battery Park back to Staten Island, each on a different weekday, although not necessarily on the same day he or she steered the ferry to Battery Park. Two or more recruits may have made the trip from Staten Island to Battery Park on the same day." You have to determine the weekdays on which each recruit (first and last names) "piloted the ferry from Staten Island to Battery Park and from Battery Park to Staten Island."

Where I run into a problem is on the last clue, #5. "Each person piloted the ferry from Battery Park to Staten Island either on the same day as or at some point later in the week than he or she guided the ferry from Staten Island to Battery Park."

When solving a logic puzzle, the first thing I do is translate the clues from "LogicPuzzleSpeak" into English, just to make it comprehensible. My translation of clue #5 is: "BS (Battery Park to Staten Island) = the same day as, or later in the week than, SB (Staten Island to Battery Park).

Keeping in mind that, according to the introduction, all these trips took place on weekdays, this clue, in my opinion, implies the following:

· BS-Friday = SB-Monday, SB-Tuesday, SB-Wednesday, SB-Thursday, or SB-Friday.
· BS-Thursday = SB-Monday, SB-Tuesday, SB-Wednesday, or SB-Thursday.
· BS-Wednesday = SB-Monday, SB-Tuesday, or SB-Wednesday.
· BS-Tuesday = SB-Monday, or SB-Tuesday.
· BS-Monday = SB-Monday

To clarify that last line: If, because every BS is the same day as, or later in the week than, its corresponding SB, and, since Monday can’t be later in the week than any other day, BS-Monday must be SB-Monday.

Moving up the list, since BS-Monday = SB-Monday, then BS-Tuesday can’t be SB-Monday, and must therefore be SB-Tuesday.

And, moving up the list again, since SB-Monday and SB-Tuesday are already spoken for, BS-Wednesday must be SB-Wednesday.

See where I’m going with this? What I wind up with is:

BS-Monday = SB-Monday
BS-Tuesday = SB-Tuesday
BS-Wednesday = SB-Wednesday
BS-Thursday = SB-Thursday
BS-Friday = SB-Friday

The problem with this is that it contradicts the information given in the other clues. Clue #1, for example, states that Stella “made the trip from Staten Island to Battery Park at least two days before piloting the ferry from Battery Park to Staten Island”.

The answer sheet doesn’t even address this contradiction, so one of us must be wrong, and it’s probably me. Can someone read this over and tell me where I made my mistake?

With tremendous gratitude,

John D. Corr

2/7/2013 8:21:25 PM

tstopp2004
tstopp2004
Posts: 2
You have forgotten the statement about two or more recruits can travel SB with only one of them being the pilot. Also SB is required, but BS is not.

2/7/2013 8:29:14 PM

tstopp2004
tstopp2004
Posts: 2
There is no contradiction. You state that Stella "made the trip". If it said Stella "piloted the ferry" there still would be no contradiction because anyone can take the trip without being the pilot. Assume they all made the trip on Monday, only one could pilot it there. The others could be passengers.

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