Mental Game by Francesco Carrara.

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If you wanted high-impact, easy-to-do magic then this is for you.

Here’s what happens:
The magician places 4 cards with numbers on both on the table.
The faces and card numbers are added together giving a different result every time a card is turned over.
After this operation we are left with a result that is exactly the same as what is printed on a letter inside the envelope.
The magician takes the cards out of the box and counts the until you reach the forecast number. This is the only card with a different back.
But that’s not all, when turning over the card that was inside the envelope with the result of the sum, now we can see that
on the other side reveals the card that is exactly the same as deck card.
This spell has 3 effects in one performance.
Fully automatic, no memorization or special moves required.