Smart People Are Stupid

Take me, for example.  I fancy myself smart, at least about math–I have a degree in the subject, and have written two books about it.

So here’s what happened.  My wife, who works in retail, asked me the following thing.  With a sales tax of eight and a quarter percent, a hundred dollar item (ticket price \$100) is going to cost you \$108.25 (taxed price).

But she and her colleagues had a bunch of items listed at taxed price, and they had to figure back to the ticket prices.  Just subtracting eight and a quarter percent didn’t work.  Why not?

Me: “Look:  say the item costs \$1,000 and the tax is ten percent.  Taxed price is \$1,100, right?  But ten percent of that is \$110.  Subtracting \$110 from \$1,100 doesn’t get you back to \$1,000, because you just took ten percent of something BIGGER.  See?”

She was persuaded.  But then: “OK, so what’s the drill?  How do I get back from the taxed price to the ticket price?”

Me:  “Why, just divide the taxed price by 1.0825.”

She:  “Huh?  What are you talking about?  What happened to percents?”

Me:  “Oh, you know, percent is just a way of saying numbers.  A hundred percent is 1.  Eight and a quarter percent is 0.0825.  So your taxed price is 1.0825 your ticket price.  Divide and you’ve got it, see?”

She:  “No.  Show me on the calculator.”

I divided by 1.0825 on the calculator.

She:  “No, show me usinmg the percent key.  I always use the percent key.”

Me:  “I don’t know what the percent key does.  Look, it’s just numbers.  Percents are just numbers in thin disguise.  It’s easier to work with the numbers.”

She:  “I want to work with percents.  I don’t really get numbers.”

That’s where we got stuck.  I only do numbers, I don’t do percents.  She only does percents, she doesn’t do numbers.  I have never in my life used the percent key on a calculator.  I don’t know what it does, and I don’t want to know.  Numbers are real, all else is illusion.  But not to my wife.  And now she thinks I’m a fraud.  All those fancy math books, and he doesn’t know how to use a percent key!

She wandered away at last muttering: “Congming fan bei congming wu“—approximately: “Smarties outsmart themselves.”  Which I guess is true.