Subtraction is the cruelest math
I just got back from a trip to the local Office Depot to buy some CD-Rs so I can back up data for the upcoming move. The total came to $8.60. I handed the cashier a $20 bill. What followed was one of the more entertaining checkout scenes I have ever witnessed. I was being attended by a trainee, although an experienced employee was supervising her. The trainee accidentally hit the “enter” button on the register instead of the “$20″ button, and so the register assumed I had paid the exact amount, and did not compute the change. The supervisor knew exactly what to do: “Just give him the change. It’s $14.40.”
Those of you playing along at home will realize, as did the trainee, that her math was a little suspect. “No, I think it’s $13.40,” she said. The supervisor got a calculator. Not believing its answer, she got out a piece of paper and pencil. Finally, after the calculator had given the same answer about three times, they decided to accept its wisdom, and the trainee counted out $11.60. At this point, they had to call over the manager to re-open the cash drawer so they could exchange one of the quarters for a nickel.
I shudder to think what would have happened were there long division involved.
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I saw far too many pharmacy students whip out calculators for “6 * 30″ and things like that to ever trust a pharmacist to do much at all correctly.
Comment by Erik J. Barzeski — June 14, 2003 @ 6:37 pm
uh, isn’t $20 - $8.60 == $11.40 ? That’s what my beowulf clustered Mathmatica says…
Comment by glenn1you0 — June 15, 2003 @ 10:46 am
Sure, it’s an easy product to compute, but if there’s an easy procedure that brings some form of mechanical reliability and makes it less likely that a tired mind will make a mistake, why wouldn’t you want the student to use the calculator? Trying to prematurely optimize is a great way to make a mistake.
Comment by Brian — June 16, 2003 @ 4:06 am
Hmm, reminds me of the time I got two dimes and nine pennies in change at Taco Bell.
Comment by Michael Tsai — June 16, 2003 @ 2:11 pm
Exactly. Even after all that, they still counted out the wrong change.
Comment by Alexei Kosut — June 18, 2003 @ 9:07 am
What ever happened to lost art of counting it back to you?
For instance,
“Ok. $11.60 (hand forty cents). $12.00. $13.00. $14.00. 15.00, and $5 makes twenty. Have a good day.”
It is nearly impossible to screw *that* up.
Comment by steve — June 18, 2003 @ 3:25 pm