My wife and I went out for a couple of slices of pizza the other night and, on the way home, I wanted some frozen custard. So we went to my favorite place, which was a little busy — as it always is when the weather’s nice.

When it was my turn, I ordered a medium concrete with chocolate custard and M&Ms. The cost used to be just under five dollars, but the price has gone up a little this year. That didn’t bother me a bit, and I was prepared.

The young woman at the counter punched my order into the cash register and told me the total was $5.18. I held up a quarter and said, “That’s for the eighteen.” With my other hand, I held up a $20 bill (all I had in my wallet) while saying, “And that’s for the five.”

She looked at me as if I had switched my order to two lawn chairs and a baby yak. With a quizzical look on her face, she hit a couple of buttons on the register, which told her she owed me $14.82 in change. I could see the number from my side, knew it was wrong, yet kept my mouth shut for a moment. But when she started counting out fourteen one dollar bills from the till, I had to stop her.

I leaned forward and said calmly, “You owe me $15.07.” She gave me the same perplexed look, and I could see her contemplating, “Well, this guy’s pretty old, he must know what’s going on.” So, she put the singles back in the drawer, pulled out a ten, a five, a nickel, and two pennies, and handed them to me along with the receipt, adding, “Math was never my best subject.”

I looked at her and said, “This has nothing to do with math! This is a data entry problem! If you had typed in the amount I gave you ($20.25), the machine would have done its job and told you the exact amount of change to give me!”

Actually, that was all in my head. I’m not the kind of person who’s going to berate a young woman over such a simple error. Yet standing there, I bemoaned hearing one more person complaining about an inability to handle numbers — what John Allen Paulos describes as “innumeracy.”

This wasn’t high-level mathematics. You don’t need to have gotten an A+ in calculus or trigonometry or even algebra to make change. There were no quadratic equations or cosines or cube roots involved. Just simple arithmetic. Subtraction: the second thing we were all taught after we learned our numbers and how to add them.

But I kept all that to myself. All I said out loud was, “Okay, thanks,” before stepping to my left a few feet to wait for my dessert.

It was delicious. Almost enough to make me forget to share this story with you. But not quite.

Previously on Harris Online…