Pre-arrangement : Remove all tens and picture cards from the deck
The magician asks a spectator to shuffle the cards. He then takes a bunch of cards and fans them in front of the spectator who is aked to pick a card from the fan. The spectator is to remember the chosen card and replace it in the pack.
The magician then asks the spectator to multiply the value of the card they picked by 2 and then after adding 5, to multiply that number by 5. The spectator is then asked to remember the total they arrive at.
Next, the magician lets the helper select another card in the deck, and that value, they are to add to the total that they had arrived at earlier. The spectator is finally asked to reveal their total to the magician.
How the Trick is Done
When you hear their total, subtract 25 ..... The two digits you get will be the two cards they chose.
Eg. if their total is 86 then thir two selected cards would have been an 8 and a six.
This is a self working mathematical trick.