Hi,



I'm embarrassed to ask this, but I have a basic question about making
percent solutions (% w/v).  I wish to make a 2.5% solution of drug A in
saline.  I have 10mg of drug A and want to know how much saline to  
add to
get a 2.5% solution.  The formula I found for making % solutions is:



%solution  = (dry mass in grams/volume in mls) *100



According to this formula, I would need to add 0.4ml to 10mg to get a  
2.5%
solution.  I am not sure whether this is correct however, as my  
intuition is
to keep the units the same (mg/mls) and here the amount of saline to be
added would be 400ml.  I know this is a bit stupid and I can only  
claim that
it is close to Friday and my brain is shutting down...Can someone  
resolve
this for me? Help!



Nicola J. Broadbent





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