So, you know that your patient needs 325 mg of atropine.
Moreover, you know that your stock solution of atropine has a concentration of
What that means is that every miligram of stock solution will contain
Convert the needed dosage from miligrams to grams by using the fact that
#325color(red)(cancel(color(black)("mg"))) * "1 g"/(1000color(red)(cancel(color(black)("mg")))) = "0.325 g"#
Looks like you needs to give your patient les than
More specifically, you need to give him
#0.325color(red)(cancel(color(black)("g"))) * "1 mL"/(0.50color(red)(cancel(color(black)("g")))) = color(green)("0.65 mL")#
If you take 65 mL of a solution that contain 0.050 g atropine per mililiter, you get a dosage of 0.325 g of atropine.