Actually it's an easy trick... You have to know which coin has THIS ONE written on it's back. And you have 5 of them. For easier understanding of the trick we will call them: the right one (one with THIS ONE at his back), and fake ones (blank background).
Tell her to put her finger on one of them (20% that she will pick the right one). She does. If that's the right one - woala. But if she puts her finger on fake one, tell her to pull the coin near her. She does that. So there's 3 fake and 1 real coins left. Tell her to pick another one. She does. Regardless if it's the real or a fake one, tell her to pull the coin next to the first one. Here we have two possible scenarios:
1) She could pick the right one. So, you have to groups of coins. One with 3 fake coins and one group with 1 fake and one real. In that case you say - OK, we'll eliminate these 3 (and you put a group of 3 fake coins in your pocket). There are 2 coins on the table - one fake and one real. Tell her to pick one of these two. So again two possible scenarios:
1a) If she picks the right one say - ok, we'll eliminate this one too (and you put the last fake coin in your pocket). And tell her to flip the coin remaining on the table and - woala!
1b) If she picks the fake one you are again doing "1a)" scenario... The only difference is that in scenario "1a)" she picked the coin that is real, and in scenario "1b)" fake one. But you know which one is real and you adjust your trick to leave exactly that one on the table.
2) She picks a fake one once again. You have two groups - one with 2 fakes, and one with 2 fakes and 1 real. Then tell her to pick another one. Again 2 scenarios:
2a) Picks a real one and moves it to a group near her with 2 fake coins. Then you say - OK, we'll eliminate these two. And you put 2 fake coins in your pocket, remaining on the table 2 fake and 1 real. Then you do all the same with the group of three coins. Tell her to pick one. If she picks the real one, eliminate other 2, if she picks fake, eliminate that one leaving 1 fake and 1 real. And do it once again.
2b) Picks a fake one and moves it to a group of 2 fake coins that she has already picked. You have one group with 3 fake coins, and one with 1 fake and 1 real. Then you can choose - to eliminate a group of 3 fake coins or to tell her to pick again from a group of 2 coins.
So the point is that you know which one is the real one, and you keep forcing it to remain last. She will not doubt and get suspicious because she has no idea how the trick should look like. Get out and get some chick with this one
