This is a card trick I find very useful when a spectator makes it impossible for you to do the trick.I call the trick ,Mathomatic.
Mathematical discovery-- ask a person to choose a card. tell him to remember it's numerical value (ace = one, jack- = 11, queen = 12, king = 13) ---also the suit of the card.
Tell them to double the value of the card
Then tell them to add three to the total
Then tell them to multiply the complete total by fi
This done ask them to concentrate on the suit
If the card is a diamond they must add one
If the card is a club they must add two
If the card is a heart they must add three
If the card is a spade they must add four
They must then tell you the final total
From it you immediately know the chosen card
The secret is to mentally subtract 15 from the given total--you will have a number of two figures- possibly three
The last figure gives you the suit(diamonds 1, clubs 2, hearts 3, spades 4.) while the first figure gives you the suit.
Example: Jack of clubs
11 doublesd is 22, add 3--25, multiply by 5--125. add for clubs--makes 127. You are told that number
Subtract 15 mentally. result 112. last figure (2) means clubs, first figure(11) means jack.