Cut a piece of white paper into a 5-by-5-inch square before you do the magic trick.
Ask an audience member to volunteer a coin for your trick. Show the crowd both sides of the piece of paper to prove that it hasn't been altered. Place the paper flat on the your magician's table and place the coin in the center.
Fold the paper almost in half, leaving about 1/2 inch between the top and the half that has been folded.
Fold the right side of the paper around the back to the halfway mark, and fold the left side back over this half.
Fold 1/2 inch of the top of the paper down so it appears that you have created a packet with no holes in it.
Hold the packet out for audience members to feel so they can determine that the coin is still in the packet. As you return to your table, with your back turned to the audience, turn the packet upside down and let the coin fall into your hand through the opening that has been left. Pick up a handkerchief and put down the coin in the same movement.
Cover the paper with the handkerchief and hand it to an audience member. Utter a magic word, lift the handkerchief and let the audience member unfold the paper to see that the coin has disappeared.
Prepare to do the trick by placing a little circle of tape on the back of a quarter. Hide the quarter in your hand before you begin the trick.
Ask an audience member to give you a dime. Hold the dime tightly between the thumb and index finger of your right hand. Slide the quarter into position behind the dime.
Use your left thumb to press the dime onto the tape-covered side of the quarter and use your left index finger to squeeze the 2 coins together.
Take the coins between your left thumb and index finger, and turn your hand so that the face of the quarter can be seen. Drop the coin quickly into your right hand so it looks to the audience like there really is only 1 coin.