chemistry I dont get it

Question

A physician ordered a dose: of cimetidine at 0.6 g the dose available is 200 mg/tablet how many tablets should be administrated?

Answer 1

The trick is in the unit conversion. There are two different units in this question and we need to convert them into the same unit. Since 1g=1000mg, convert the 0.6g to 600mg, which is the same unit as the tablet. 600mg/200mg=3 tablets.

Answer 2

The trick is to let the units be your friend. Line them up so that units on the top will cancel with units on the bottom and yield the result you are looking for, Since we start with grams, we need to use a conversion factor that has grams on the bottom so we can cancel out "grams" to get rid of it. So we use 1000 mg = 1 g or a conversion factor ratio of 1000/1. Then we need to use a second conversion factor that has "mg" on the bottom to get rid of the "mg" we just introduced. So we use 1 tablet = 200 mg and orient it so the "mg" is on the bottom. That leaves units of "tablets" which is what we want (we are asked for the number of tablets). Then you just multiple and divide the numbers as they are laid out.