THE INDEX SECTION
Price & packs
A four-pack price needs a four-piece denominator
The current official single and yellow four-pack are nearly equal per item.
Count bodies, refills and colors separately
A mixed pack can have several useful quantities rather than one universal count.
An assorted pack may not cover a single-color target
Total pieces and required-color pieces are different denominators.
Three dated official US offers, with different selling units
A complete gel pen, a gel refill and a highlighter are three distinct purchases.