Here are some of the areas which I remember using math:
1) Blood Bank - RhIg dosing, CCI, chance of finding a particular unit of blood
2) Chemistry - Creatinine clearance, LDL, Henderson-Hasselbach
3) Statistics - Sensitivity, specificity, positive & negative predictive value
4) Lab Management - General accounting
I'm sure there's probably more. Feel free to add to my list.
----- Antony