Innumeracy

I've had a post about innumeracy floating in my head for a while, and I would have written it today (and it would have been brilliant) but Blogger has not seen fit to let me log in until just now, when I have about five minutes left before I leave to pick up WonderGirl and Rocco.

So, until I have a chance to write it, I leave you with a motivating example from this morning:

I go to a local store to exchange a piece of clothing. (DT bought me a very cool sweater thing for Mother's Day - it was crocheted/see-through and sparkly and hip. Unfortunately, it fit WonderGirl better than me.) As we are in no-returns-land, I look around for something similarly styled (but that will fit both arms at the same time). Eventually, I find another sweater that is (of course) more expensive.

For the sake of the example, let's say that sweater 1 was $20 and sweater 2 was $30. The store clearly doesn't have an automated inventory system through the register - it's the kind of place where prices are hand-written on little stickers. The saleslady is (also clearly) panicking about how to deal with the price difference. I offer that she could just charge me $10. She insists that this will not work because of tax. Yes, I say, but add tax to $10 and it will be right. This is, apparently, unacceptable.

After an inordinate amount of scribbling on an old receipt and several aborted attempts to use the register as an adding machine, she finally comes up with this: I will be given credit for $20 plus tax (say $21). The difference between this and the price of sweater 2 is $9, so she will charge me $9 plus tax.

Although I tried again to persuade her that she was undercharging me, she was so relieved to have come up with an answer that she remained resolute. Her store lost a dollar and I had to listen to her laugh about math being confusing.

Why is this so common and why doesn't it bother us?