Often medical solutions expressed as a percentage are not really a percentage as such. A percentage is the ratio of two quantities with the same units.

Here, the context given by the problem suggests the "25%" solution is really (25 g)/(100 mL). That is, the units are grams and milliliters--different units.

With that assumption, we want to find the volume (v) of solution needed to deliver 6 g of medicine. An appropriate proportion* is ...

v/(6 g) = (100 mL)/(25 g)

v = (6 g)(100 mL)/(25 g) = 24 mL

So, the total volume of the infusion is ...

250 mL +24 mL = 274 mL

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* The concentration is given in terms of g/mL, but we have used a proportion that is mL/g. The reason for that is we want the variable to be in the numerator of the ratio. The variable here represents volume, so we have written the proportion with volumes in the numerators.

Having the variable in the numerator means the equation can be solved in one step--by multiplying by its denominator.

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3 years ago