Adapted from Mathemagical Showtime! Investigating the Math Behind Numerical Magic Tricks - www.amazon.com/Mathemagical-Showtime-Investigating-Behind-Numerical/dp/0970445911
Ask the audience for a 3-digit number.
Then instruct the audience to multiply the number 3-digit number by 7.
Then multiply that product by 11.
Then multiply that product by 13.
The magician should write down the answer immediately in a place that the audience can't see.
Compare the magician's answer to the audience's answer.
How did the magician compute the result so rapidly?
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