Hi Doppler,
It's not Binary, Binary would work like this:
27 / 2 1st guess narrows down to 13.5 say 14 cards or say 13 whatever
14 / 2 = 7 2nd guess narrows to 7 cards
7/2 3rd guess narrows to 3.5 cards
3.5/2 4th guess still not guaranteed to have it! depends how you split 3.5, 1 or 2
Hi Lo game is Binary and goes like this, say the secret number is 1
You guess 13, high
you guess 6, high
you guess 3, high >>>> you still need to guess!
you guess 2, high
This card game is done in 3 clues! (and you need all 3, again unlike Binary) Binary still has a ways to go for worst case scenario.
And you are missing the coolest part, putting the card anywhere in the deck. So that at the end of the guessing you count out the "mark's" favorite number of cards and THERE you find his card in the deck. There is no more fooling around after the 3 clues, the card is found at the mark's number in the deck.
I saw the 21 cards trick just before this trick and this trick is 2 x's cooler at least!
Here check the link: