November 21, 1988 12:00 PM

To be a mathematical genius, you have to remember a few basic rules. For instance, Cher is 64. Well, actually, 64 is Cher. But 644 is Juror. Easy, isn’t it? Now you try it.

Yes, by applying a few common-sense guidelines, you too can amaze friends and impress total strangers with your astounding feats of mathematical magic. Do long sums, squares, cube roots and more in your head.

Well, maybe you can’t, but Arthur Benjamin can. Benjamin, a 27-year-old graduate student at Johns Hopkins University in Baltimore, has been a “mathemagician” for audiences around the country for the last four years. “It’s just like being a great concert pianist or tennis player,” Benjamin says, without excessive modesty, of his lightning-quick mathematical reflexes. As for occasional mistakes—Benjamin folds them right into the act, arguing, “It’s no worse than a juggler dropping a ball.”

Now hang in there. There will be a fairly easy explanation of the Cher trick very soon. Before that, it is important to know that Benjamin believes his ability is an acquired skill and not just some freakish natural talent. His big secret is a combination of calculating from left to right and mnemonics—a process by which he assigns phonetic sounds to numbers. By giving the sound ch to 6 and the sound r to 4, for instance, he can recall 64 by thinking of ch-r, which he pronounces chair or, whimsically, Cher. When working on a problem, Benjamin transforms large numbers into his code names and stores them in his mind while moving on to the next mathematical step.

Benjamin, the Cleveland-born son of Larry, an accountant, and Lenore, a special education teacher, revealed his inclinations early. “When he was 4, he taught himself how to multiply,” says Lenore, “because when he pressed the right combinations on his toy cash register, the drawer opened.”

Benjamin, who will graduate in May with a Ph.D. in mathematical sciences, plans to teach college math. He’ll continue his public performances, though. So the next time you need to calculate the six-week interest at 17.9 percent on a $249.47 credit card purchase, shout it out to Benjamin. He’s one of those guys you can count on.

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