Heard of binary numbers? They are the numbers that computers use to make the words and pictures you see on your screen. Not only can they be used for that, they can be used to perform magic tricks with your class. Choose a number between 1 and 31, give a child five cards with a set of numbers on them, give the cards back with their chosen number. Get the student to blow on the cards and they share the number with you that they chose. These students are under no illusion – Maths is magic!