here's a fool-proof way to do all these types of problems.
gr (1 ml
) (.. 60 mg
6.... (15 mg) ( 1 gr ) = 90 = 0.67 ml
first you cancel out gr's and then mg's. ml is left and that is what you want to be left so remember to always put your desired label in the numerator and set the rest of your problem up so that you can cancel out your undesired labels (gr and mg).
i added my conversion factor (60 mg = 1 gr) into my problem and then multiply accross.
in this case i multiplied 1 x 1 x 60 = 60
then in the denominators 6 x 15 x 1 = 90
then i divided, 60 divided by 90 = 0.67:d
this will work with all simple dosage calculations. i could be wrong so someone finding otherwise- please feel free to correct me!