Write it out:
Convert grains to milligrams first. 5 Grains = 325 Milligrams.
Milligrams to Grains conversion
(This link can help you with some conversions.)
So, now we write the problem out. I am doing it the long way, to prevent error.
Remember that the 1st and 3rd units of measurement in this equation have to match.
300 m.g. : X tabs :: 325 m.g. : 1 tab
(So now we drop the symbols. Remember, what ever you do to one side of the equation, you must do to the other. We are solving for X.)
300 : X :: 325 : 1.
Multiply your means first, then your extremes:
X times 325 = 325X Underline that, and to the right of that, multiply 300 X 1
So 325X = 300. Now divide both numbers by 325, because that is the number next to X and we are solving for X.
We need to get X by itself.
After you do that, divide the 300 by 325 = 0.93 tabs. So unless the Pharmacy can chop it up for you, you will end up giving a whole tab. Hope I haven't confused you further!