Reading the Comics, May 14, 2015: At The Cash Register Edition


This might not be the most exciting week of mathematically-themed comic strips. But it gives me the chance to be more autobiographical than usual. And it’s got more reruns than average, too.

Also, I’m trying out a new WordPress Theme. I’m a little suspicious of it myself, but will see what I think of it a week from now. Don’t worry, I remember the name of the old one in case I want to go back. Also, WordPress Master Command: stop hiding the option to live-preview themes instead of switching to them right away.

Epic Customer Fails: a customer insists a product, Regular $50.00, now 40% off, is ten bucks, not thirty.
Norm Feuti’s Retail For the 11th of May, 2015.

Norm Feuti’s Retail (May 11) led off a week of “Epic Customer Fails” with an arithmetic problem. My own work in retail was so long ago and for so short a time I don’t remember this happening. But I can believe in a customer being confused this way. I think there is a tendency to teach arithmetic problems as a matter of “pick out the numbers, pick out the operation, compute that”. This puts an emphasis placed on computing quickly. That seems to invite too-quick calculation of not-quite the right things. That percentages are a faintly exotic construct to many people doesn’t help either.

My own retail customers-with-percentages story is duller. A customer asked about a book, I believe an SAT preparation book, which had a 20 percent (or whatever) off sticker. He specifically wanted to know whether 20 percent was taken off the price before the sales tax (6 percent) was calculated, or whether the registers added the sales tax and then took 20 percent off that total. I tried to reassure him that it didn’t matter, the resulting price would be the same. He tried to reassure me that it did matter because the sales tax should be calculated on the price paid, not reduced afterward. I believed, then and now, that he was right legally, but for the practical point of how much he had to pay it made no difference.

He judged me warily, but I worked out what the price paid would be, and he let me ring the book up. And the price came out about a dollar too high. The bar code had a higher price for the book than the plain-english corner said. He snorted “Ha!” and may have told me so. I explained the problem, showing the bar code version of the price (it’s in the upper-right corner of the bar code on books) and the price I’d used to calculate. He repeated that this was why he had asked, while I removed the wrong price and entered the thing manually so I could put in the lower price. And took the 20 percent off, and added sales tax, which came out to what I had said the price was.

I don’t believe I ever saw him again, but I would like the world to know that I was right. And the SAT prep book-maker needed to not screw up their bar codes.

Continue reading “Reading the Comics, May 14, 2015: At The Cash Register Edition”

Create a Graph: Something To Play With


I realize that I’m probably about eight years behind the curve on this one, but I only just learned that the National Center for Education Statistics has this cute little create-a-graph application (Flash required), good for whipping up several of the name-brand graphs out there.

The pie chart is particularly nice since I’ve never figured out how to make pie charts in Octave (it’s probably some tricky command like ‘pieplot’), and they have a neat historical resonance because they were turned from one of the many obscure tools of the then-obscure field of statistics into the first rank of mathematical tools by Florence Nightingale. She used them as a way to communicate, efficiently, what the causes of death in the Crimean War were.

This gives me use a fine narrative hook in class: I can ask them if they know who first made pie charts famous, and then insist they do indeed, they just never had any idea about it.