# pharmacy math question

by Magda
(Frisco, tx)

A patient needs IV infusion of 0.9% NaCl. You have a 1L Sterile Water For Injection bag and 4.5% w/v stock solution of NaCl. Considering that there are no volume displacement effects; How much of the 4.5% w/v needs to be added to the 1L SWFI bag to produce the desired concentration?

A. 700mL
B. 250mL
C. 350mL
D. 500mL

### Comments for pharmacy math question

 pharmacy math by: Anonymous Use an equation, with single missing variable.What you have = What you wantC - concentration V - volumeC1 x V1 = C2 x V21000(0.00) + X(0.045)= 1000(0.009)Then do the MATH0.045X = 9X = 200mL

 Hey anonymous...missed a step by: Jerry Yes, you take what you have, and equate it to what you want.=> First, what do you have:1000mL of waterThat will be written as- 1000(0.0)and,you have 4.5% - but don't know how much needed.This unknown variable will be X(0.045)=> Next, what you need:1L of water PLUS unknown amount of X that together contains 0.9% concentration:[1000 + X](0.009)Now, put it together:1000(0.0)+x(0.045)=(.009)[1000+X]0 + 0.045X = 9 = .009XSubtract .009X from both sides.036X = 9Divide both sides by .036X = 250