Here’s a puzzle: if a company adds more of an item to a package and advertises that you “get X items” or get X ounces free,” don’t they have to keep the price the same? Well, no. I suppose not. Reader Scott found this fascinating example of fuzzy math on various packs of undershirts at Walmart.

He writes:

I was in to purchase undershirts for work when I stumbled on an interesting fact. Wal-mart has a pack of 6 for 13.96 and then another pack that says 2 free shirts but is charging 4.50 more. What is the purpose of saying free when in fact it is not?

Let’s see. The package of six undershirts was originally (though I have my doubts) a five-pack. The eight-pack is a six-pack with an additional two shirts offered “free.” Let’s break it down.

\$13.96 divided by 5 shirts = \$2.79 per shirt
\$13.96 divided by 6 shirts = \$2.32 per shirt

Meanwhile, the six-pack with two free, or eight-pack, technically offers the best deal, but not by much.

\$18.46 divided by 6 shirts = \$3.07 per shirt
\$18.46 divided by 8 shirts = \$2.30 per shirt

The price we shirt isn’t all that different here, but this is similar to other cases we’ve seen of a “free” item having a different SKU and getting priced dynamically without taking the first item into account.