How many grams of drug powder would you need to weigh to prepare 32ml of a suspension that should have a strength of 20mg/ml?

The answer is 0.64 g of drug powder.

Explanation:

Let "x" be the grams needed to prepare a 20 mg/mL mass concentration solution, let "V" be the volume of the solution, in this case 32 mL, therefore the mass concentration will be equal to:

mass concentration = x/V

Clearing x, we have:

x = mass concentration * V = (20 mg/mL) * (32 mL) = 640 mg

one gram is one thousand milligrams, therefore, we have:

640 mg * 1 g/1000 mg = 0.64 g

15 grams for the drug powder