# The 10p napkin scam

You take a napkin and fold it into a perfect square. Pop it on the table and dump a load of 10p pieces on the table beside it. Challenge your friend to a dynamic game of wits and cunning. One by one each of you will place a 10p onto the napkin. The first person who can’t place their 10p piece on the napkin without going over the edge loses. Simple game, simple rules, and a simple way to always win this animated game of strategy.

Two important tricks will ensure your victory in this classic deterministic algorithm computational scam. Yes, it’s a hustle, so use it with care!

## Do unto others

Its all about matching moves. Mathematicians would call it symmetry, psychologists would call it mirroring, computer scientists would call it set x=y. Get the first part right and victory has to follow. It’s totally predictable.

## Step by step

The first step to ensure victory is a little sneaky, even though your opponent will never spot it. Make sure that when you fold the napkin, you fold it into a square and that you know where the exact centre is. Here’s a hint: if you folded your paper twice diagonally to make it into a square, it will be where the two diagonals cross.

Next give your opponent the chance to go either first or second. Their free decision on this determines your next move. This is called setting the initial conditions. Any computer program needs to be initialised – the values of the core data need to be set before the program can run – but here there are slightly different conditions depending on what your opponent decides. Don’t worry, they won’t notice this part either.

IF they decide to go first THEN pretend you ‘forgot’ one other rule. Tell them you need to place a 10p coin exactly over the middle of the square, then do exactly that.

IF they decide to go second THEN place your first coin exactly on the centre. Either way, you’ve ended up with a coin right in the centre for your opponent’s first move.