Pharmacy Math Cheat Sheet Cheat Sheet (DRAFT) by bnoland

When to use: when you have to mix two solutions of different concen­tra­tions to prepare a final solution of the required concen­tra­tion.

What to do:Make a grid with the goal solution in the middle, the lower strength % in the lower left, and the higher strength % in the upper left. Subtract across to the opposite corners of the grid. Add the two resultant parts of both % strengths and the result is the total parts ratio needed to make the desired strength. Now figure out how much of each solution should be added to equal the final concen­tra­tion:

"­Prepare 1000mL of 40% solution of amino acids using 70% amino acids and 30% amino acids soluti­on."­

70 |  ­  |10 (meaning 10 parts of the 70%)
---------
 ­ ­ ­ ­ |40|
---------
30 |  ­ ­  | 30 (meaning 30 parts of the 30%)

10 + 30 = 40

Needed volume from the problem is: 1000mL / 40 = 25mL per part.

Take the values from the grid:

10 X 25mL = 250mL of the 70% solution.
30 X 25mL = 750mL of the 30% solution.

(Checking: 750mL + 250mL = 1000mL)

Simpli­fied: 1 part 70% solution to 3 parts 30% solution, or 1:3 70%:30%.



How much of each solution should be added to the concen­tra­tion?