Shampoo for My Shaved Head & A Lesson in the Metric System

Today I stopped by my local Sport Clips to get some more shampoo. Yes, even shaved heads need to be washed with quality shampoo. Trust me, it's that much more important when people can see every inch of your scalp. I go with the Paul Mitchell Tea Tree stuff. At first, I liked it for the tingly sensation, but I guess my head is way too cool for that now because I don't feel a thing when I use it. But my hair always looks great (ha ha ha, I know) so I continue using it.

As I perused the shampoo selection and various sizes, I noticed a 1L mega size alongside my usual 500ml size. Since there were no prices on them, I asked the girl behind the counter what the price difference was between the two sizes. She told me, and even though the larger size contained twice as much as the other size, the price was a little less than double. I said something along those lines more to myself than to her and she said, "No, it's three times the shampoo." I was a bit confused by her statement because I learned the metric system in elementary school and 1L = 1000ml = 2 x 500ml. I pointed this out and she said, "Hmm, I learn something new every day." To downplay my intellectual superiority and to make her feel better for not knowing, I said, "Well, if you tell people it's three times as much, maybe you'll sell more." Now I wonder to myself whether she'll do just that or try to impress people with her newfound knowledge of the metric system...