Got a friend with an iPhone? Here's how to scam an easy free drink off them. This week's trick caomes to us all the way from Argentina! It's a simple yet baffling trick you can play on anyone who has an iPhone or an Android phone. First, write down a prediction. Then as your marks for a string of numbers: their birthdate, address, dress size, anything numeric. Multiply them all together. Hit equals, and show them the result. Then show them your prediction: the very same number. Baffling!