Mo. Rev. Stat. § 413.155: Packages containing random weights to state price per single unit of weight.

In addition to the declarations required by section 413.145, any package being one of a lot containing random weights of the same commodity, at the time it is offered or exposed for sale at retail, shall bear on the outside of the package a plain and conspicuous declaration of the price per kilogram or pound and the total selling price of the package.