LANCE BURTON'S SECRETS OF MAGIC:
"THE BIRTHDAY TRICK"
This is a great mathematical trick that is generally presented as a puzzle, but it takes on a whole different meaning when it's performed as a mindreading effect.
The magician turns his back and has someone write down on a piece of paper the year of their birth. Below this, he has them write down the year in which an important event occurred in their life. Below this, he has the person jot down their current age and below this he has them write down the number of years that have passed since the important event occurred. He has them draw a line below the figures and asks to have the figures totaled. The magician turns around, and correctly announces the total.
SECRET: This is a very old mathematical trick. If you add the year of the person's birth to his present age, it will naturally result in a total that equals the date of the present year. The same thing holds true for the year of an important event and the number of years since it happened. Therefore, when the four figures are totaled, the answer will always be double the present year.
Note: If the person hasn't celebrated their birthday yet, then the total will be double the present year minus one. In order to avoid this problem, it is wise to ask the person the month they were born before starting the trick. If their birthday for the present year has not occurred then subtract one
year from the total.
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