This is one of my favourite tricks to perform BECAUSE it is so very simple that anyone can do it. It is not necessary to utter a lengthy prologue like I do, but--I feel that the seeming complexity of the premise helps to conceal the common sense of the technique. The humility and the amateurishness of the act at first threatens to disenchant the audience but--if you can hold them till the end, they'll be completely dumbfounded.
I apologise (as always) for the poor quality of the video (and audio).
Take heart and be assured that your presentation will at the very least, be more entertaining than mine!
https://www.youtube.com/watch?v=yjBYpexlRzc