# Simple Formal Logic Riddle

by Ubern0va
Tags: formal, logic, riddle, simple
 P: 60 Lets assume that the old saying "nice guys always finish last" is true. A running race is held around the block with five people competing. Two nice guys are in the race. To finish the race, a runner must cross through a gate fit to hold only one person at a time. Who will finish last? Under what conditions? OOps forgot to mention, for clarity's sake that all persons competing in the race have the intention of winning. The first part is pretty obvious if you take everything said above literally, but you must solve the second portion to solve the entire riddle. I made this up myself, and I'm just learning preliminary formal logic, so forgive me if later it turns out that I phrased something wrong. Though I think everything is ok, I'm really not sure.
 Math Emeritus Sci Advisor Thanks PF Gold P: 39,568 Assuming "good guys" finish last And there are two "good guys", then they both finish last. As to what that means you will have to decide for yourself. You didn't tell us what "finish last" means here!
 P: 60 Yes I should probably define finishing, it's a bit ambiguous at the moment, leading you to the incorrect answer. Lets pretend that there's a gate fit for one person to pass through at a time. We will call passing through this gate "finishing". Who finishes last? Not so simple now huh? Also, to clarify, the condition is the answer to the riddle, if you have to leave the condition to be decided by me then you have the wrong answer :P
 Sci Advisor HW Helper P: 2,586 Simple Formal Logic Riddle The slowest non-nice guy finishes last, assuming there is a slowest non-nice guy.
 P: 496 It seems that it depends on how "nice" the two nice guys are. The nicer of the two would be the one who would finish last... or you would end up with a strange "oh no, you go ahead and finish ahead of me" argument between both nice guys.
P: 60
 Quote by AKG The slowest non-nice guy finishes last, assuming there is a slowest non-nice guy.
But nice guys always finish last. That is, if there is a thing (in the domain) who is a guy, and who is nice, that guy always finishes last.
P: 60
 Quote by motai It seems that it depends on how "nice" the two nice guys are. The nicer of the two would be the one who would finish last... or you would end up with a strange "oh no, you go ahead and finish ahead of me" argument between both nice guys.
The statement is not that "the nicest guy always finishes last". The degree of niceness of each guy is not discussed in the saying; this ambiguity is what makes this a riddle. Though it isn't the key to the asnwer, which is purely logical.

That argument can't happen because it is stated in the riddle that it is the intention of each runner to win the race.
 Sci Advisor HW Helper P: 2,586 Your premises are contradictory, thus I can prove that anyone finishes last regardless of the conditions (aside from the ones given in the problem). You state that nice guys always finish last. This means that if x is a nice guy, then x finishes last. There are (at least) two nice guys in the race, so both of them finish last. Therefore, neither one finishes before the other, so they finish at the same time. Thus they both pass through the gate at the same time. But only one person can pass through the gate at a given time, so we've reached a contradiction. So I can prove that anyone finishes last. However, the question itself is unanswerable because there is no situation that could possibly model your situation (because it would have to model a contradiction, i.e. a contradiction would have to be true).
 P: 60 Hint: There is a way to bypass the contradiction. You were so close in your explanation, I can't believe you didn't come to the right conclusion. I thought you had it untill I read your post fully. :P HUGE Hint (via random example): Every person has exactly one father. Bill is the father of Jake, and Bob is the father of Jake. What can be said about bill and bob? The very fact that this seemingly contradictory riddle has an answer should signal that there is some trickery involved, again, it is a riddle not just a question, think outside the of the box (but still in formal logic terms).
 Sci Advisor HW Helper P: 2,586 Under the condition that 2 = 1, the nice guy finishes last? If this is the answer, you should note tha saying that "two nice guys are in the race" means that there are indeed two (distinct) nice guys in the race, and the above is not a sensible way to say that "there is one nice guy known by two names in the race." Two actually means two, not one with two names.
 P: 17 since each of the 5 people in the race aim to win the race, and nice guys always finish last, hence, one of the 3 not nice guys will win the race and one of the 2 nice guys will finish last. anyway, its unimportant who will finish last!
 P: 60 AKG, yes that is more or less the answer. Except it's not that two equals one, that can never be. It's that one guy is the equivalent of the other guy, i.e. they are the same person. However, your point is dually noted, I may try to change the riddle so that it implies that two guys are in the race instead of just coming right out and saying it. That way we can bypass the fact (which I just realised) that my premises state that 'there is a nice guy in the race, and there is another guy who is nice, and in the race, and is not equal to the first nice guy'. Perhaps I should use something similar to that father example I gave. That way there can be two names for the same person, but I never say that there are two guys (in the domain) such that each of them is in the extension of the predicate 'is nice'. Thanks for the input AKG. I see you also realized that the answer is right there in the premises for those who didn't get the first part if the premises state that 'nice guys always finish last, and that there can only be one person who finishes last, then the answer can only be that the nice guy finishes last'. It comes directly from the premises.
HW Helper
P: 2,586
 Quote by Ubern0va AKG, yes that is more or less the answer. Except it's not that two equals one, that can never be. It's that one guy is the equivalent of the other guy, i.e. they are the same person.
If "they" are the same person, then there are not 2 nice guys in the race, but you said there were. Again, "two" means "two", not "one with two names."
 However, your point is dually noted
For your interest, you mean "duly", not "dually."
 Perhaps I should use something similar to that father example I gave.
Yeah, that would work better.
P: 60
Yes, thank you for that reiteration. :P

 Quote by AKG For your interest, you mean "duly", not "dually."
Again, thank you for correcting me (you take joy in this I imagine), I was not complete until this very moment. Give me a break, its one of those words I've not used twice in my entire life.