In the magic kit you will find a chart showing two diamonds on one side and five on the other. If you take this letter hiding one of the rhombus of the bottom you can make it appear that it is the one of diamonds , if you catch it at the other end seems to be three, on the other hand if you do it just looks like the four six of diamonds . You'll have to practice this trick enough to not notice as your finger covers the rhombus space correctly. The faster you change the number of diamonds in the letter, more will your audience dumbfounded .