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Strange calculations

Topics/tags: Miscellaneous, short

Tonight I took the counselors from the Craft of Code camp out to dinner [1]. They deserved a nice dinner. It’s been a long week. Every day started before 8 am, ended after 6 pm [2], and was filled with nine- and ten-year-old children [3]. Many of the counselors also did additional work in the evening to prepare the next day’s curriculum or materials.

But my awesome counselors are not the subject of this musing. Rather, I’m musing about the bill from dinner.

The first bill I received from dinner had a subtotal of some number of dollars and 22 cents. It also had an automatic gratuity of 20% [4], which was some number of dollars and 84 cents. The total? Some larger number of dollars and 7 cents.


If you add two even numbers, you should get an even number. If you add 4 cents and 2 cents, you should get six cents. So I started to look more closely at the bill, which, while expensive, seemed comparatively cheap. I counted the number of entrées. There were eight. But I was pretty sure that we had fourteen people. So I recounted. It seemed that six meals were missing.

As you might expect, I talked to the wait staff [5]. They said that it had printed two sheets of receipts but they only brought me one. They went back to get the other. I never got the other half. However, I did eventually receive a new bill. This one added correctly and included all of the meals.

But I’m a pain, so I asked them about the addition of four cents and two cents on the original bill. Their response? Yeah, the iPad software we’re using doesn’t always work so well. It also doesn’t work well with parties of more than eight people.

I’m not sure how to react to those statements. I will check my bills carefully whenever I visit that restaurant, though.

Postscript: I also purchased a to go meal for a family member. I forgot to check over that bill. I should have. The subtotal was $13.99. The gratuity was $2.80. The sales tax was $0.98. And the total?

The total was $17.76.

While I’m happy to celebrate the birth of the US [6], I’m pretty sure that the total should have been $17.77.

I really do want to understand how those kinds of addition errors happen in the software. How are they representing numbers? And why do these programmers still have a job?

[1] Since team bonding dinner is part of our budget, arguably the College took the counselors from the Craft of Code camp out to dinner.

[2] Ah, the joy of non-hourly student workers.

[3] I’m pretty sure that every one of the counselors said something like I now have much more respect for elementary school teachers at some point during the week.

[4] I’ve heard rumors that accounting changes tips to 18%. I wonder if that really happens. It certainly hasn’t seemed to happen, but I haven’t been paying enough attention.

[5] It’s tempting to take these kinds of accidental discounts, but it’s wrong.

[6] Or whatever we associate with 1776.

Version 1.0 of 2018-06-22.