BY CALCULATIONS HOW WOULD I PREPARE 200ml of 80% GLYCEROL (V/V)

Answer 1

80% glycerol (v/v) means 80 mL glycerol/100 mL solution.
So place 80 mL glycerol in a 100 mL volumetric flask and add water to make 100 mL. (That makes only 100 mL soln--I assume you can double all that and use a 200 mL volumetric flask?)

Answer 2

160ml