Big John, a card shark, puts three cards face down on a table. One of the cards is an ace; the other two are face cards. You place a finger on one of the cards, betting that this card is the ace. The probability that you've picked the ace is clearly 1/3. Big John now secretly peeks at each card. Because there is only one ace among the three cards, at least one of the cards you didn't choose must be a face card. Big John turns over this card and shows it to you. What is the probability that your finger is now on the ace?

That's a real dilly, Soot!
I've seen it before (different guise) so I'll "watch"!

For independent events, conditional probability..P(A|B)=P(A)P(B)/P(B)=P(A)=1/3

I like it manXman ... you are correct