Pre-arrangement : Remove all 10s and picture cards from the deck of cards
The magician asks a spectator to shuffle the cards. He then takes a bunch of cards and fans them face-down in front of the spectator who is asked to take a card from the fan. The spectator is to remember the chosen card and replace it in the pack.
The magician asks the spectator to multiply the value of the card they chose by 2. Then, after adding 5, they must multiply that number by 5. The spectator is asked to remember that number.
Next, the magician lets the helper select another card in the deck. They must add the value of that to the total they had arrived at earlier.
Finally, the spectator is asked to reveal their total to the magician.
It’s actually very simple. When you hear the total number, just subtract 25.
The two digits you get will be the two cards they chose.
For example, if their total is 86 then their two selected cards were an 8 and a 6.
This is a self working mathematical trick.