This depends on the volume of the 40 percent solution you have. The question can be rewritten as: 40%a/(a+b) = 3% where a is the volume of the 40% solution, and b is the volume of water we need to...
All percentages are in mass% and all quantities are in grams (mass), be sure do not to take volumes into account because mass is 'additive', volumes are not quantitatively additable! Answer: Take...
If you mean: % by MASS ( %m/m), it's quite easy to do (based on the 'Mass Conservation Law). Measure 10 gram of the 95%m/m original solution, this contains 95% of 10g = 9.5g Solute Then add new...