One of the easiest tricks an up and coming magician can try is the telephone number magic trick. This simple illusion involves taking advantage of little-known mathematical peculiarities.
Gathering an Audience Member
Pick a member of the audience and have them head up on stage. Ideally, you'll have a sidekick who doesn't mind sharing their phone number to the group; be sure to announce that you intend to guess your assistant's phone number.
Making the Calculations
With a calculator, have your assistant type in the first three digits of their 7-digit phone number, ignoring the area code. Be sure not to peek at the calculator in advance. Multiply the number by 80, add 1 and then multiply the sum again by 250. Have your assistant add the last four digits of his or her phone number twice and then subtract 250 before returning the calculator to you. Following these calculations with the imaginary phone number 123-4567 would bring you to a total of 2,468,134.
Reveal the Result
With the calculator in hand, wave a wand over the screen while discreetly dividing the number on the device by 2. If the math was calculated correctly, the number left on the calculator will be your assistant's phone number.