The Five Card Trick

This trick makes you look like you're a mind reader! In fact it's just the sort of thing to scare away AN EVIL GOLLARK from the planet ZOG.

First you need to make up the five special cards like the ones here:

You'll see they are numbered 1 - 5 in BLACK on one side and 6 - 10 in RED on the other side. Make sure that the "6" is on the reverse of the "1" and the "7" is on the reverse of the "2" and so on.
The cards can be any size you like, but if you're going to carry them round, make them credit-card size.

You're now ready to play your trick!

• Pass the five cards to a friend and then TURN YOUR BACK! You are going to do the whole trick without even looking!
• You ask your friend to drop the cards one by one on the floor.
• Ask your friend to tell you how many RED cards are facing upwards.
• Ask your friend to add up the total showing on all five cards.
• But before your friend has finished - you can shout out the answer!
• Remember - you haven't seen the cards at any point since you started the trick!

THE SECRET:
If your friend says there are NO red cards, the total will be 15. (Because if all the black numbers are showing the total must be 1+2+3+4+5 = 15.)
If there are any red cards showing, you ADD an extra 5 on for every red card.
So if your friend says there are 2 red cards, you add 2 x 5 = 10. This would make the total 10 + 15 = 25. It would not matter which two cards are red!
Of course if ALL the red cards were showing, the total would be 15 + 25 = 40.

You can probably do this trick two or three times before they start to guess the secret!

Links:

Tricks and Games

The Murderous Maths main index page