Can someone help with these drug calculations?

I am about to start my second semester and we were given these to work on for practice.
Can someone explain the way they would figure these 3 questions out. I know the answers but im having a hard time figuring them out, I think I might be making them harder than they really are. I can't find problems like these in my dosage and calculations book either.
Thanks everyone, any help would really be appreciated.
3. Order: Administer 500 mg of Theophylline in 250 ml of D5W.
Available: The pump is set at 13 ml/h.
How many mg is the patient receiving per hour?
4. Order: 1 liter of Normal Saline with 20,000 units of heparin to infuse at 42 ml/hr.
How many units of heparin per hour will the nurse be infusing?
5. Order: Administer 7 units per hour of regular insulin IV.
Available: Regular insulin 50 units in 100 ml of 0.9 NaCl.
The nurse would set the pump at how many ml per hour?
Answers are
3. 26 mg/hr
4. 840 units/hr
5. 14 ml/hr 
Aug 15, '06Ok, here is the first one...
First you need to figure out how many mg is in 1 ml so you take
500mg X mg
______ X _________ = 250X = 500 then 500/250 = 2mg/mL
250 mL 1 mL
then you take 2 X 13 = 26mg/hr 

Aug 15, '063. mg/ml = 500/250 = 2. 2 x 13 = 26.
4. 20,000units in 1000cc = 20,000/1000 = 20 (20units/cc). 20 x 42 = 840.
5. 50 units in 100cc = 50/100 = 0.5units/1cc. If 1cc = 0.5units, 7units (per hr) = 14cc. 
Aug 15, '06Here is the second...
First you need to find out how many units of heparin are in 1 mL of Saline...
20,000 units X units
___________ = ________ = 1000X = 20,000 = 20,000
_______
1000 mL 1 mL 1000
That equals 20 units per 1 mL, then you just 20 X 42 and that is
840 units per hour 
Aug 15, '06I was just going to reply but it looks like I was just beat to the punch
So just 'ditto' to what has already been said and best of luck to you! 

Aug 16, '06here is how to solve these using dimensional analysis (factor/label method).
3. order: administer 500 mg of theophylline in 250 ml of d5w.
available: the pump is set at 13 ml/h.
how many mg is the patient receiving per hour?
first, establish what labels you want to end up with. that will be mg/hr, where mg is in the numerator and hr are in the denominator. next, you set up a serious of fractions, which are actually ratios which are designed to cancel out all the labels except for the ones you want to be left with (mg/hr). so, here is how you set up this problem:500mg / 250ml (what you have on hand) x 13ml/1hr (rate of infusion) = 6500mg / 250ml (after doing the math and canceling out the ml labels) >reduce to 26ml/hr
4. order: 1 liter of normal saline with 20,000 units of heparin to infuse at 42 ml/hr. how many units of heparin per hour will the nurse be infusing?
again, the labels you want to end up with are units/hour. you are also going to need one conversion factor for 1 liter = 1,000 ml. here is how you set up this problem by dimensional analysis:20,000units / 1liter (what you have on hand) x 42ml / 1hour (given infusion rate) x 1liter / 1,000ml (conversion factor) = 840,000units / 1,000hour (after doing the math and canceling out the liter and ml labels)reduce to 840 units/ hour
5. order: administer 7 units per hour of regular insulin iv.
available: regular insulin 50 units in 100 ml of 0.9 nacl.
the nurse would set the pump at how many ml per hour?
the labels you want to end up with are ml/hr. here is the set up:100ml / 50units (what you have on hand) x 7unit / 1hour (given rate of administration) = 700ml / 50hr (after doing the math and canceling out the unit labels, reduce to) = 14ml / hr

Aug 16, '06Quote from daytonitethis is how they taught us and it is soooo easy this way! i have always stunk at math, but i have been making 100% on my dosage tests with this method! once you get the process, you can figure any problem out!here is how to solve these using dimensional analysis (factor/label method).
first, establish what labels you want to end up with. that will be mg/hr, where mg is in the numerator and hr are in the denominator. next, you set up a serious of fractions, which are actually ratios which are designed to cancel out all the labels except for the ones you want to be left with (mg/hr). 

Aug 16, '06Just wondering what you have to make on your drug dosage calculation test? My school is now requiring a 100% with 2 chances and then you are out!! What are other schools requiring. Thanks for any input.

Aug 16, '06Quote from Bonny619You are very welcome. I hope this helped to explain a logical way to get to the answers for you.Daytonite, thank you!!!

Aug 16, '06I believe we are 90%, we have to take a 10 question math test every semester, but someone said the final course you need them all right.