alligation

noun

al·​li·​ga·​tion ˌal-ə-ˈgā-shən 

: a process or rule for the solution of problems concerning the compounding or mixing of ingredients differing in price or quality:

a

: one applied when a definite mixture is required

called also alligation alternate

b

: one applied when the price or quality of the mixture is to be determined

called also alligation medial