You have a 12.5% w/v solution and a 3% w/v solution in stock. What volumes of each solution do you need to mix to make 855 mL of a 7% solution? Please round answers to the nearest whole number.

Step 1. Set up the alligation grid. Higher strength: 12.5% Lower strength: 3% Desired strength: 7% Step 2. Calculate the parts. Parts of 12.5% solution = 7 - 3 = 4 parts Parts of 3% solution = 12.5 - 7 = 5.5 parts Total parts = 4 + 5.5 = 9.5 parts Step 3. Calculate volumes for 855 mL. Volume of 12.5% = (4 / 9.5) x 855 = 360 mL Volume of 3% = (5.5 / 9.5) x 855 = 495 mL