Thursday, August 17, 2006

Guess Your Birthday !

Here's a fun trick to show a friend, a group, or an entire class of people. I have used this fun, mathematical trick on thousands of people since 1963 when I learned it. Tell the person (or class) to think of their birthday...and that you are going to guess it.

Step 1) Have them take the month number from their birthday: January = 1, Feb = 2 etc.
Step 2) Multiply that by 5
Step 3) Then add 6
Step 4) Then multiply that total by four
Step 5) Then add 9
Step 6) Then multiply this total by 5 once again
Step 7) Finally, have them add to that total the day they were born on. If they were born on the 18th, they add 18, etc.

Have them give you the total. In your head, subtract 165, and you will have the month and day they were born on!

How It Works: Let M be the month number and D will be the day number. After the seven steps the expression for their calculation is:

5 (4 (5 M + 6 ) + 9 ) + D = 100 M + D + 165

Thus, if you subtract off the 165, what will remain will be the month in hundreds plus the day!

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Saturday, August 05, 2006

Card Trick

Here's a real clean card trick that is bound to amaze and surprise your friends.

Have a friend shuffle a standard 52-card deck to his satisfaction. The ask him/her to turn over, face up, a pile of twenty-five cards. As they count out the cards to twenty-five, act like you are intensely memorizing every single one of them in order. In truth you are only interested in the 17th card in the pile. Memorize that 17th card..

Turn the twenty-five card pile over, now face down, and set aside.

Take the remaining cards and do the following:

If it is a two through nine card, place it face up, and count out cards up to the number ten. For instance, if you turn up a six, you would place it face up, and then count out four cards coming down, saying "Seven, eight, nine, ten." If you turned up a three, then seven cards, saying "Four, five, six, seven, eight, nine, ten."

If the card you turn up is an ace, ten, or picture, tell your friend that you must have cards 2 through nine for this trick and place the card on the bottom of the deck, face down like the rest of the cards. (Someone told me that aces and pictures work too, but I haven't verified it yet.)

Repeat this procedure until you have completed four columns of "ten counts."

Take whatever remaining cards you have after making the four columns, and place them face down on TOP of the twenty-five card pile you set aside earlier.

Now ask your friend to total up the numbers at the top of the four columns.

Say the total was 23. Counting from the very top of the set-aside-pile-plus-remainder-cards, state you are interested in the 23rd card. Just before turning over the 23rd card, state that it is the 17th card that you memorized at the beginning of the trick!

If you did everything correctly, it works every time! Amazing!