Dosage Calculation Assistance

Hello, I have a problem with one specific area in dosage calculations and that is, when I am asked how many ml of a substance will I add to the bag. Here is a specific problem:
On hand: 500ml bag of 5% dextrose in .2 normal saline and KCL 20 meq/10ml and microdrip (60 gtt/ml)
Ordered: IVs 500 ml of 5% Dextrose in .2 normal saline over 8 hours with KCL 4meq/100ml
How much (ml) KCL will you add to the 500 ml bag?
On hand: 500 ml bag of 5% dextrose in .2 normal saline and a vial of Aminophylline 250mg/10ml
Ordered: IVs 5% dextrose in .2 normal saline with Aminophylline 25mg/100ml to run @ 50ml/hr
How much (ml) Aminophylline will you add to the 500 ml bag?
Any assistance will be greatly appreciated with this!!!! Thanks in advance! 

Jul 22, '09this really isn't much different than if the "bag" were a human being that was getting the injection. instead of putting the injection of kcl or aminophylline into a human being, you are diluting it first into an iv bag and then dripping it slowly into the human being. look. . .
on hand: 500ml bag of 5% dextrose in .2 normal saline and kcl 20 meq/10ml and microdrip (60 gtt/ml)
ordered: ivs 500 ml of 5% dextrose in .2 normal saline over 8 hours with kcl 4meq/100ml
how much (ml) kcl will you add to the 500 ml bag?
you are first being told about the 3 items needed to prepare and give this medication to the patient. the microdrip tubing isn't relevant to the question you need to answer.on hand: 500 ml bag of 5% dextrose in .2 normal saline and a vial of aminophylline 250mg/10ml
dose desired: 4 meq/100 ml of iv fluid, but because of the total amount of iv fluid on hand that it will need to be mixed in is 500 ml, it changes the dose desired to 5 times what it was, or: 20 meq/500 ml (4 meq/100 ml = 20 meq/500 ml)
dose on hand: kcl 20 meq/10 ml (potassium usually comes in 10 ml or 20 ml vials like this from which you must withdraw the amount you want and mix it into the iv bag)
now, calculate using the formula dose desired divided by the dose on hand multiplied by the amount the dose on hand comes in to get the amount to give. . .20 meq (dose desired)/20 meq (dose on hand) x 10 ml (amount the dose on hand comes in) = 10 ml (amount of kcl you will add to the 500 ml bag of d5w and 0.2ns)
ordered: ivs 5% dextrose in .2 normal saline with aminophylline 25mg/100ml to run @ 50ml/hr
how much (ml) aminophylline will you add to the 500 ml bag?
this is the same kind of problem. . .
dose desired: aminophylline 25mg/100ml, but because of the total amount of iv fluid on hand that it will need to be mixed in is 500 ml, it changes the dose desired to 5 times what it was, or: 125 mg/500 ml (25mg/100 ml = 125 mg/500 ml)
dose on hand: aminophylline 250mg/10ml
calculate using the same formula used above. . .125 mg (dose desired)/250 mg (dose on hand) x 10 ml (amount the dose on hand comes in) = 5 ml (amount of aminophylline you will add to the 500 ml bag of d5w and 0.2ns) 
Jul 22, '09Thank you soooo very much!!!!!! You explained it so well!!! I really, really, really appreciate all your assistance! I get it now!!! Thanks again!!!!