81 dimes: a Math Panic

My yard sale coin collection
 in a canning jar with a funnel

All winter long, I save up dimes and quarters for yard sale season.  Last Saturday, I was out-and-about with my quarters in my left pocket, dimes in my right, when I happened upon a family selling some DVDs I thought my boys would like, $1 each.

When I started counting out quarters and dimes to pay her, the woman's eyes lit up.  "I LOVE dimes!" she gushed.  We talked long enough that I knew she meant it, so after I paid her (in dimes), I emptied out my right pocket, handed her all the rest of my dimes, and told her I'd be back after I checked out the yard sales further up her street.  She could count the dimes and give me dollar bills in exchange.

When I came back, there was a small pile-up of shoppers on her porch; she hadn't had time to count.  She handed the dimes to her husband who counted them out in front of me.  And then [watch it: here comes the math moment], he got a stricken look and asked, "that's 81 dimes.  Um, how much money would that be?"

How much money is 81 dimes?  You might expect that I'd rant about the stupidity of not knowing the answer.  But I want to take the opposite view; that the guy could figure out the answer, but he had a very common attack of Brain Freeze.  A moment of Math Panic.  It happens to us all.  You've had Math Panic.  I (who teach math for a living) have had Math Panic.  We all have Math Panics, at times.

A burst of Math Panic can be expensive.  It can be expensive on the large scale:  you get a sales pitch from that guy selling time shares and don't realize until later that his math doesn't match your budget.  It can be expensive on the small scale:  you're at the store and your friends are waiting, so you grab the more expensive barrel of pretzels by mistake because the pricing is so complicated.   A recent study by marketing professor Michael Tsiros at the University of Miami School of Business shows that this kind of grocery store math-anxiety-ignorance costs shoppers a lot of money.

My dime exchange interaction had all the ingredients leading up to the big brain freeze.  

• First of all, it was an unexpected problem, one that was sprung on this guy last-minute.  Almost nobody (but me) carries a pocketful of dimes around, so he hadn't been thinking about dime-to-dollar conversions at all.  
• Secondly, there was an audience for his math: not only was a crowd milling around, but I was standing there, staring at him.  It's very hard to think about both people and numbers at the same time, and for most of us, people win over math.
• Third, there was time pressure.  He felt like he had to answer right away, because I had already been waiting a little while.  

All of which says, if you're faced with a purchase that has math involved, you should know that Math Panic Happens.  If you can prepare yourself for the math beforehand, fabulous.  But if not, do everything you can to give yourself more time and to get away from the observant eyes of other people.  Tell the salesman you need to go home and think about it.  Tell your friends you'll be there in 5 minutes, and send them off to look for root beer.

And most of all, don't let that moment of Math Panic be your boss.  It's easy for us all to think we're just too stupid to handle certain problems, to let that sense of stupidity define us and establish the way we do things.  I remember once freaking out over my taxes.  Finally, I realized, "Miser Mom; you have a PhD in Math.  If you can't do taxes, nobody can!"  So I took a deep breath, slowed down, and did those taxes with almost no problem.  Just, slowly.

In the same way, we can all decide that the moment of "Oh, shoot, I don't know the answer!" is not the real us.  The real us is someone who is patient, persistent, and smart.  That arithmetic:  just do it.