A pharmacist needs to obtain a 70% alcohol solution. How many ounces of a 30% solution must be mixed with 40 ounces of an solution to obtain a 70% solution?
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A mother solution or a pure solvent can be diluted down to give a lower solution; but you can't dilute down to give a higher concentration, i.e. to go from 30% to 70%. We don't know whether it is v/v% or m/m% .