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And now for my next trick…

February 20, 2009

I come from a family of civil engineers, growing up I was the only one in the house who read books with more words than numbers in them. Needless to say, my love for literature was viewed in much the same way one would view a family member who decides to join the Hare Krishna- they smiled at my growing stockpiles of books and waited for the day the youthful indiscretion would be outgrown naturally.

I’m happy to report they stopped waiting years ago, probably after calculating that the odds were not at all in their favor.

Remember that scene in My Cousin Vinny where Marisa Tomei explains, “My dad’s a mechanic, my uncles are mechanics, my brother’s a mechanic..,” when asked what qualified her as an expert witness on automobiles?  Well, I’m neither an engineer nor a mechanic, but in some ways the love of numbers rubbed off on me. To this day a math problem remains the best way to clear my head.

It does not, however, do anything for hang-overs. For that you need massive amounts of water and aspirin.

My dad’s favorite math parlor trick for us kids goes this way:

  • Think of a number between 1 and 10 and keep it to yourself
  • In your head, multiply the number by 5
  • Add 50
  • Subtract 2
  • Add 273
  • Add 63
  • Subtract 48
  • Subtract 144
  • Add 56
  • Subtract 126
  • Subtract 122
  • And finally, divide by five
  • This last number is the one you picked

This enthralled us to no end until about age ten when we realized he never could say what that selected number was. At which time he sagely pointed out that we learned math is all about relationships; operations have inverse counterparts that cancel each other out. I guess that’s a lot less daunting than teaching us calculus straightaway.

I appreciate its brilliance more now as I torture my own kids with the same “magic trick”. For one thing, as long as they don’t catch on right away, the problem can grow along with them. You can have them pick a number between 1 and 100 for instance. Or do exponents and squares. As long as you can keep the numbers straight in your own head, they’ll never be the wiser.

On second thought, you might actually want them to catch on sooner rather than later. If they’ve turned 25 and are still clueless, you’ve got problems.

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