secrets-of-mental-math-malestrom

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Prologue
in on his secrets of “math genius.” With these skills, almost anyone
can do what Art Benjamin does every time he gets on stage
to perform his magic.
This particular night at the Magic Castle, Art begins by asking
if anyone in the audience has a calculator. A group of engineers
raise their hands and join Art on the stage. Offering to test
their calculators to make sure they work, Art asks a member
of the audience to call out a two-digit number. “Fifty-seven,”
shouts one. Art points to another who yells out, “Twenty-three.”
Directing his attention to those on stage, Art tells them:
“Multiply 57 by 23 on the calculator and make sure you get
1311 or the calculators are not working correctly.” Art waits
patiently while the volunteers finish inputting the numbers. As
each participant indicates his calculator reads 1311, the audience
lets out a collective gasp. The amazing Art has beaten the
calculators at their own game!
Art next informs the audience that he will square four twodigit
numbers faster than his button-pushers on stage can
square them on their calculators. The audience asks him to
square the numbers 24, 38, 67, and 97. Then, in large, bold
writing for everyone to see, Art writes: 576, 1444, 4489, 9409.
Art turns to his engineer volunteers, each of whom is computing
a two-digit square, and asks them to call out their answers.
Their response triggers gasps and then applause from the audience:
“576, 1444, 4489, 9409.” The woman next to me sits
with her mouth open in amazement.
Art then offers to square three-digit numbers without even
writing down the answer. “Five hundred and seventy-two,” a
gentleman calls out. Art’s reply comes less than a second later:
“572 squared is 327,184.” He immediately points to another
member of the audience, who yells, “389,” followed by Art’s
unblinking response: “389 squared will give you 151,321.”