Here is the solution to the Johnson-Laird "probabilistic" king-ace problem:

---
	If one of the following assertions is true then so is the other:

		(1) There is a king in the hand if and only if there is an
		ace in the hand.

		(2) There is a king in the hand.

	Which is more likely to be in the hand, if either:  the king or
	the ace?
---

It would seem that "If one of" is ambiguous between "If at least one of" 
and "If only one of," and for that reason alone it would not be published
in a test of reasoning. (That which ETS couldn't publish I would not
recommend for use with subjects if anything will be said about their
reasoning skill/capacity based on their performance on the item.)
Fortunately, in this case it makes no difference: either way, you could
obviously prove K & A in the cases where

	(1)	(2)
	T	T
	T	F
	F	T

so everthing must boil down to the F F case.  It's easy here to do a proof
that can get A (constructive dilemma and reductio), but ~K instead of K. 
Ergo, the answer must be A. I don't see the illusion.  Where is the
illusion?  Now of course people who haven't learned how to reason can't
reason, and since most people haven't learned how to reason, most people
will bomb on this problem.  Most technical philosophers have learned how
to reason (should be some at Princeton, I hope :) ), so they'll
get this one (as you yourself predict).

Cheers,  //Selmer Bringsjord  selmer@rpi.edu  www.rpi.edu/~brings