frobbiness new puzzles up... check 'em out.
Michael H. Pryor
SPOILER!!!!
Tim Keating
Heh, the title sort of gives a mean hint to everything. Was it the subconsious effect of the hint, or your massive brain-power honed by constant lovin' contact with the Machine? ;-)
Red Davis
SPOILER SPACE FOR PART THE SECOND:
rOD
I don't think you need to turn over the E.
Jonno Downes
You only need to turn over the 5 and the F. The 5 to prove that the letter on the other side is a vowel, and the F to prove that the number on the other side is not odd. The rule says that an odd number must have a vowel, but it doesn't say that a vowel must have an odd number, so the E card doesn't need to be checked. Likewise, the rule also says nothing about the letter accompanying an even number, so the 2 doesn't need to be checked.
Greg Shoom
Don't feel bad if you got either of these wrong... the success rate in the general population is something like 5%. I'm serious. See the Shafir paper I referred to.(http://www.joelonsoftware.com/news/fog0000000352.html) - there's a good theoretical reason why humans make these mistakes.
Joel Spolsky
Ah, I may be being dumber than usual, but the first question, as phrased, is apparently unanswerable.
Matt Clark
The answer to part two is "Two cards, the card showing 5 and the card showing F". Nobody cares about the E or the two, as there is no rule that relates to their opposite faces. We have to verify that '5' has a vowel on the other side, and that 'F' does not have an odd number on it's opposite side.
Matt Clark
Do excuse me, where above I said:
Matt Clark
Matt,
John Lemitz
I got the first part right, after about 5 minutes of thought. My first impression, though, was absolutely backwards. After about two minutes, I decided that it was partly indeterminate, and then I figured it out.
Jeff Paulsen
John, you are too right! Goes to show I should never take part in an interview at midnight either...
Matt Clark
Most people have discussed about the second part, and little else must be said there (yes, the correct answer is that you need to flip two cards).
Alberto Molina
Ooooooppppsss!!!
Alberto Molina
Actually, I think it unlikely that top-notch coders will do statistically significantly better than average at the card-flipping task (properly called the Wason card task or problem) - if I recall correctly, other highly logical types have been tested and fall out at the same rate. The problem is that the examples used (numbers and letters) are abstract. There's some interesting research in cognitive science on the difficulties abstractions have for human reasoning. It turns out that if you replace the abstract rules with social rules (I'll give an example in a second), people do much much better.
Ben Scofield
To answer Matt's question, I think that the first sentence of Part I clearly limits the universe of possible shapes to the four specified.
Beth Linker
Here's another way to think about it...frobbiness demonstrates an exlusive-or relationship between the characteristics of two shapes. If we call white "true" and black "false," and circle "true" and triangle "false" (the values are completely arbitrary, and not important to the solution), then a white XOR triangle = true, and black XOR circle = true. Remember, if the value is "true" that means it's the same as the shape our questioner is thinking of - if false, it's different. Now, assign the opposite values. white is false, black is true, circle is false, triangle is true. white XOR triangle = true, black XOR circle = true.
Mark Ashton
Interesting problems. I think I might have gotten some inadvertent help on the "frobby" puzzle by reading Joel's discussion on his site about thinking through disjunctions. As a result, some neurons may have fired in my brain that wouldn't have otherwise.
Paul Brinkley
If I'm not mistaken, part II says:
Maxim Pogorelov
Actually, my take on it would be only the 5 and F need to be flipped.
Craig Fruth
So we can generalize frobbishness to mean that the set of items which are frobbish with the defining entity posses some but not all of the attributes of the defining entity. In such a case it may be necessary to further breakdown frobishness into n-frobbishness where an entity has exactly n of the specified attributes. Obviously one cannot be frobbish to an entity with only one attribute.
Hamish Muirhead
Frobbieness is simply the XOR truth table...
Del Miller
Considering I'm a vegetable with a capital S, I think I've got rather decent skills in English. However, I've yet to find 'frobb'y in any dictonary. Thus I take it to be:
Lennart Fridén
Frobby is a nonsense word - (AFAIK anyway :)
Greg Mitchell
"Frobby" is probably an allusion to "frob":
Paul Brinkley
Concerning the second puzzle:
Andy Shyne
Andy Shyne, the puzzle stated "what is the minimum number of cards you should turn over to prove the rule is true" so although you're quite right in that we only need to turn over one card in order to prove that the rule is false (if it is) we still need to turn over two cards in order to prove it true.
Lennart Fridén
Ben's comments were interesting but a bit counter-intuitive, so I wish more information were available.
Gary Chatters
the second puzzle is solvable by the logic proposition :
shailesh kumar
the second puzzle was easily solved by the proposition that : if a implies b then ~b implies ~a.
shailesh kumar
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