The grandparent's note about units and your mention of ratios get at the same problem for me: The lesson mixes two of the physical world concepts that are ofte

The grandparent's note about units and your mention of ratios get at the same problem for me: The lesson mixes two of the physical world concepts that are often modeled by fractions. One is an incomplete whole (the six pack) and the other is the proportions of a mixture (table demographics). Fractions always have the same rules, but the rules map differently to the different territory being modeled.