HELP w/math prob????

You are ordered to give Nitroglycerine gr 1/150. The pharmacy has supplied 0.4mg/tablet. How many tabs should you give?

I know that 1 gr = 60 mg (exception being Tyl)

Why am I drawing a blank on this problem? Thanks for any help!!

60 divided by 0.4 = 150

The 0.4 mg tablet represents 1/150 of 60 (1 grain)

The 0.4 mg tablet represents 1/150 gr

do you agree?

0.4 mg tab of NTG is equal to 1/150 grain

start by figuring how many grains in each tablet:

you're given that each tablet has 0.4 mg and you know that 1 grain is 60 mg. therefore:

[a] 0.4 mg/tab x 1 gr/60 mg = 0.4/60 gr/tab

now, clear the nasty decimal from the numerator (divide the numerator and the denominator by 0.4 each) :

0.4/60 gr/tab = (0.4/0.4) / (60/0.4) gr/tab = (1)/(60/0.4) gr/tab

[c] (1)/(60/0.4) gr/tab = (1)/(150) gr/tab

recognize in that:

1. anything divided by itself = 1
   
2. if you divide the numerator and the denominator by the same value (e.g. 0.4 in this case), you're not changing the value because you're essentially multiplying by 1.

recognize in [a] that:

1. the units are consistent: mg/tab x gr/mg = gr/tab because the mg terms cancel.

(and now that i've posted i see that daytonite has beaten me to the punch :trout:)

I found a link to a website with all of the apothecary conversions.

http://www.tostepharmd.net/pharm/clinical/measurement.html

Question? Has any nurse actually run into an order written in the apothecary system? I learned it to pass the class but will I ever have to use it?