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.

Donald tries to work as a cashier. He's not very good at change.
Disney’s Donald Duck for the 11th of May, 2015. Rerun from sometime much farther back.

Meanwhile, in Disney’s Donald Duck (May 11, rerun), Donald has some trouble making change.

Michael Fry’s Committed (May 11, rerun) plays on the fantasy of being two-dimensional in a three-dimensional world. Certainly a two-dimensional kid in normal space would be invisible, not just in one direction but from a whole wedge of space where Tracy’s cross-section is too small to notice. There are a couple fields of mathematics one can talk about from here. One of projective geometry, how shapes alter when they’re restricted to or imaged on particular surfaces. It’s a neat field that I admit I don’t have much experience in. But let me take this chance to point again to this nice web site about visualizing four-dimensional structures. It talks about many of the challenges in presenting something of dimensions in lower ones.

Another mathematics field is measure theory, the study of how much volume (or area, or length) one set has within another. This one I’m more comfortable with. A two-dimensional figure like Tracy here has no volume, in three dimensions. But in two dimensions she might have an area. The measure of a thing, how much space it takes up, depends on the figure and the space it’s trying to fill. And there can be wonderful, non-intuitive results. For example it’s possible to have a continuous curve — so that if you had perfect pen and paper and a steady enough hand you could draw it — which curls around so much that it fills area.

Mickey Mouse has to give some kids money because there's no way four of them can see a movie for 35 cents each if they have just the one dollar.
Disney’s Mickey Mouse from the 13th of May, 2015. And also from the 7th of September, 2013, so use that to calibrate your rerun clocks.

Disney’s Mickey Mouse (May 13, rerun) is a bit about using the form of a word problem to get more money out of a grownup. I thought it looked familiar and indeed, this strip ran as recently as the 7th of September, 2013. So this might be a guide to how long it takes to rerun their Mickey Mouse comics. Considering the comic strip ran from 1930 to the mid-1990s it seems like they could have more than twenty months of strips to rerun. (I can’t find a clear date when original Mickey Mouse and Donald Duck comics stopped being made.)

Jeff Parker’s Wizard of Id (May 13) does the joke about algebra being useless. I am aware that anachronistic-modernity is a building block of The Wizard of Id and don’t normally complain. (It’s also a building block of its sibling strips like B.C. and Hagar the Horrible.) But much of the work of “medieval” wizard types — astrologers, mathematician-philosophers, physicians seeking ultimate cures, alchemists — would be arcane calculations. That work would look more like algebra than anything else to the modern eye. His work would be steeped in algebra. Except, of course, that the Wizard isn’t all that good at wizarding. Overpromoted incompetence is another of the building blocks of The Wizard of Id (and much else in life).

'Florence Nightingale was the first to do what?' 'Tell a patient his HMO wouldn't cover a procedure.'
Gary Brookins and Susie MacNelly’s Shoe for the 14th of May, 2015, just missing the anniversary of Florence Nightingale’s birth.

Gary Brookins and Susie MacNelly’s Shoe (May 14) is a resisting-the-problem joke. This one’s about what Florence Nightingale was the first to do. I’ve mentioned her mathematical connection in the past. She wasn’t the first person to use pie charts and histograms to show statistical data. William Playfair pioneered most of them. But she made them famous. She gave charts about why people died in the Crimean War (disease caused by poor sanitation) or India (disease caused by poor sanitation) or the cities of the time (disease caused by poor sanitation). She is justly famous for nursing and for social reform. She also deserves fame for explaining scientifically important results in accessible ways. Sadly the strip missed the 195th anniversary of her birth by two days.


Author: Joseph Nebus

I was born 198 years to the day after Johnny Appleseed. The differences between us do not end there.

10 thoughts on “Reading the Comics, May 14, 2015: At The Cash Register Edition”

    1. Well, what do you mean by a theory? Since governments started raising money by selling annuities they’ve studied how long people are likely to live, and how many are likely to die — and from what causes — in any given area in a given year. That’s in some sense a theory of how and when people do die. And demographers study how people move about, and what for; that would look at where and why.

      That’s whole populations, though. And it’s the somewhat strange idea that we could say pretty reliably that (say) 300 people in this area will die over the coming year, but have no idea of which ones, or just when in the year they would. We can use that for individual predictions, though: if you’re a person of this age range, and have this set of medical conditions, and so on, then we can find a group of people you’re generally like and suppose you’ll live about as long as typical for that group.

      On an individual body experience, studying the mathematics of how bodies work — how nutrients and oxygen are spread out, how the body’s cells reproduce and decay and even die, how they thrive and how they break down — is a lot of good work to be done too. In graduate school I even did a course on medical mathematics, although that studied more very specific topics like how to infer how nerve pulses flow around the heart from the signals provided by an electrocardiogram. That is a theory about how bodies work, and why, although that might not be quite what you’re thinking of.


  1. When I saw the 1st comic I thought I have to share my retail story :)) : P
    One of my favorite clothes shops had a big 50% off in the window… I went in and decided to buy a dress, obviously :))) and looked on the label: old price £180, new price £120. I went to shop assistant and asked if all the prices are reduced by 50% or just some items. She so cheerful said that all of them. So, I thought it was a mistake on the label. Decided to buy the dress after all :P
    At the till the lady really smiling and happy told me the dress is £120 and started talking with me randomly. She even asked my what I study at the university and told her I am doing math :P I asked about the old price. She said £180. I looked at her like a small curios child and asked: so after 50% off the dress is £120? She said: yes. When I asked how much is 50% from 180 she blocked. Her face turned red and she used a calculator to find out. After that she panicked and I ended up helping her calculate the 50% off for all the shop because apparently I was faster than her with a calculator.
    I felt sorry for her that day, but after a couple of hours of doing this I got a new friend and the dress for free ^_^


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