At the very beginning of the trick, give 2 small bags to 2 different spectators and an envelope sealed with a padlock to a third one. The deck is shown and spectators can see it is normal and mixed.

You ask one of the spectators to remix the deck. The deck is turned over then spread in a ribbon, so that each spectator takes hold of one part. Nobody can know the cards he holds, neither himself nor you. The spectators separate their red cards from the black.
The two first spectators count the number of red cards and black cards they hold, then open the bags you previously gave them. They contain the exact amount of chips: red and black!

The third spectator is now asked to open the padlock... in vain. You then ask him to try to open it with the 4 numbers corresponding to the number of red and black cards from his 2 mates. The padlock opens and he can himself pull out a third prediction on a piece of cardboard is written the amount of red and black cards from his packets. He can check everything is correct. Impossible?