Answer: The unit rate is: " 1.5 patties / bun " ; or, write as: "1.5 patties per bun" . _____________________________________________________ The mistake is that the problem shown is incomplete.
The "unit rate" would be the "number of patterns per [single] bun." _________________________________________________________
30 patties/ 20 buns = 3 pattern/ 2 buns;
= (3/2) patties/ bun = 1.5 patties / bun ; or, write as: "1.5 patties per bun" . __________________________________________________________